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At least 199 records · Page 11Linked to original sources
PubMed1995

Genetic stability of cold-adapted A/Leningrad/134/47/57 (H2N2) influenza virus: sequence analysis of live cold-adapted reassortant vaccine strains before and after replication in children.

We previously reported that the A/Leningrad/134/47/57 (H2N2) cold-adapted virus (A/Len/47) used in preparing reassortant live attenuated vaccines for children acquired 14 (11 coding) mutations in genes coding for proteins other than haemagglutinin and neuraminidase during cold-adaptation. Preservation of these mutations in genomes of viruses isolated from children on the second, fifth, or eighth day after vaccination was examined by sequence analysis. The sequence data demonstrated that all nine coding mutations selected for examination were conserved in the genomes of all 11 strains investigated, indicating that the mutations accompanying cold-adaptation and attenuation of the A/Len/47 master vaccine are highly stable.

Acclimatization↗
PubMed1988

Morphological differences in hearts of rats well adapted and poorly adapted to chronic hypoxia.

We carried out an experiment to analyze morphological differences in hearts of rats well adapted and poorly adapted to chronic hypoxia. Male and female Wistar rats, 1 week, 4 weeks and 9 weeks old, were employed on the assumption that adaptive ability was dependent on age and sex. These rats were raised at an altitude of 2,400 m and were kept for 7 to 9 weeks. Control groups were maintained at an altitude of 600 m during the same period of time. Each group consisted of 4 to 6 rats. At the end of the experiment, body weight, heart weight, ratio of heart weight to body weight and hematocrit were measured, and ventricular wall thickness, myocardial fiber diameter, capillary supply and mitochondria were morphometrically studied. Of the 6 experimental groups, the 4-week-old male rats (M2) had the highest body weight, as compared with the other experimental groups. In addition, relative to these other experimental groups, the following features were found for M2. Heart weight was intermediate, heart weight/body weight ratio was low and hematocrit was also low. Ventricular wall thickness was intermediate in the right ventricle (RV) and interventricular septum (IVS) but was thin in the left ventricle (LV). Myocardial fiber diameter was intermediate in the RV, large in the IVS and small in the LV. Capillary supply was intermediate in the RV and dense in the IVS and LV. Mitochondria were small but cristal density and percentage area, estimated from electron micrographs, were found to be high.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

One-year follow-up of automatic adaptation of the rate response algorithm of the QT sensing, rate adaptive pacemaker.

Optimal functioning of a rate adaptive pacemaker depends upon reliable sensing of the sensor and appropriate programming of the rate of response algorithm. QT sensing pacemakers use data derived from the endocardial electrogram in the programming of the rate response algorithm. In the latest versions of these pacemakers, programming of the rate response algorithm may be performed using either a semiautomatic Fast Learn (FL) procedure or by using the newly developed, fully Automatic Slope Adaptation (ASA) mechanism. We report our experience in a prospective study of 17 patients in the first year postimplantation. ASA was characterized by significant changes only in the values of the slope settings at the lower rate limit (3.7 msec/msec at time 0 to 5.77 msec/msec at 2 weeks, P less than 0.001) during the first 2 weeks after its enablement. Further adaptation between weeks 2 to 4 was observed (5.77 msec/msec to 6.4 msec/msec, P = 0.2) but this was not significant. The slope settings derived using the FL procedure were also checked at 2 and 4 weeks and were reproducible. They were closest in value to the values attained by the automated mechanism at 4 weeks. This suggests that the final value of the slope setting at the lower rate limit using ASA is reached between weeks 2 to 4. Both methods of slope determination result in satisfactory and similar rate response profiles but the time to achieve slope stability will necessarily be slower with ASA.

Algorithms↗
PubMed1996

Adaptation-induced enhancement of vibrotactile amplitude discrimination: the role of adapting frequency.

Two-interval forced-choice tracking was used to measure amplitude discrimination for 20-Hz vibrotactile test stimuli presented to the thenar eminence of three human observers. For all observers, relative difference threshold could be decreased by adaptation to a 20- or 100-Hz stimulus. Maximal enhancement of discrimination occurred when the amplitude of the adapting stimulus was such that it excited the NP I system to approximately the same degree that the test stimuli did. A signal detection analysis determined that shifts in the observers' criteria could not consistently account for the enhancement of amplitude discrimination. A more likely explanation, in view of recent physiological discoveries, is that under optimal conditions of adaptation test stimuli differing slightly in amplitude become more distinctive because CNS events underlying the resultant sensory experiences become more refined and stimulus specific.

Adult↗
PubMed1981

Adaptation to prolonged beta-blockade of rabbit atrial, purkinje, and ventricular potentials, and of papillary muscle contraction. Time-course of development of and recovery from adaptation.

Groups of littermate rabbits were treated for various periods up to 6 weeks with twice daily subcutaneous injections of saline, D-propranolol, DL-propranolol, or metoprolol, the latter two at doses equivalent to those used in clinical therapy. Investigations were made at a sufficient time (20-24 hours after the most recent dose) to ensure that the drugs would have been eliminated from the body, so that any observed changes would represent an adaptation to treatment, not effects due to the presence of the drugs. The ECG was recorded in vivo at regular intervals during treatment. After several days, Q-Tc was prolonged by the beta-blockers, reaching a peak effect at about 3 weeks from the start of treatment, and returned to control values at 3 weeks after cessation of treatment. Action potential duration, measured in vitro by intracellular recording, was also prolonged uniformly in atria and ventricles over a similar time-course, unrelated to cardiac frequency, but shortened in distal Purkinje cells. Peak tension was not altered in propranolol-adapted papillary muscles, but the relationship of rate of rise of tension was steeper. It is concluded that these effects represent a myocardial adaptation to prolonged beta-blockade.

Action Potentials↗
PubMedDate not supplied

Adaptive optics for vision: the eye's adaptation to point spread function.

PURPOSE: Despite the fact that ocular aberrations blur retinal images, our subjective impression of the visual world is sharp, which suggests that the visual system compensates for subjective influence. If the brain adjusts for specific aberrations of the eye, vision should be clearest when looking through a subject's typical wave aberration rather than through an unfamiliar one. We used adaptive optics techniques to control the eye's aberrations in order to evaluate this hypothesis. METHODS: We used adaptive optics to produce point spread functions (PSFs) that were rotated versions of the eye's typical PSF by angles in 45 degrees intervals. Five normal subjects were asked to view a stimulus with their own PSF or with a rotated version, and to adjust the magnitude of the aberrations in the rotated case to match the subjective blur of the stimulus to that seen when the wave aberration was in typical orientation. RESULTS: The magnitude of the rotated wave aberration required to match the blur with the typical wave aberration was 20% to 40% less, indicating that subjective blur for the stimulus increased significantly when the PSF was rotated. CONCLUSION: These results support the hypothesis that the neural visual system is adapted to an eye's aberrations and has important implications for correcting higher order aberrations with customized refractive surgery or contact lenses. The full visual benefit of optimizing optical correction requires that the nervous system compensate for the new correction.

Diagnostic Techniques, Ophthalmological↗
PubMed2004

Differential requirement for adapter proteins Src homology 2 domain-containing leukocyte phosphoprotein of 76 kDa and adhesion- and degranulation-promoting adapter protein in FcepsilonRI signaling and mast cell function.

The adapter molecule Src homology 2 (SH2) domain-containing leukocyte phosphoprotein of 76 kDa (SLP-76) is essential for FcepsilonRI-mediated signaling, degranulation and IL-6 production in mast cells. To test the structural requirements of SLP-76 in mast cell signaling and function, we have studied the functional responses of murine bone marrow-derived mast cells (BMMCs) expressing mutant forms of SLP-76. We found that the N-terminal tyrosines as well as the central proline-rich region of SLP-76 are required for participation of SLP-76 in FcepsilonRI-mediated signaling and function. The C-terminal SH2 domain of SLP-76 also contributes to optimal function of SLP-76 in mast cells. Another adapter molecule, adhesion- and degranulation-promoting adapter protein (ADAP), is known to bind the SH2 domain of SLP-76, and cell line studies have implicated ADAP in mast cell adhesion and FcepsilonRI-induced degranulation. Surprisingly, we found that mast cells lacking ADAP expression demonstrate no defects in FcepsilonRI-induced adhesion, granule release, or IL-6 production, and that ADAP-deficient mice produce a normal passive systemic anaphylactic response. Thus, failure to bind ADAP does not underlie the functional defects exhibited by SLP-76 SH2 domain mutant-expressing mast cells.

Adaptor Proteins, Signal Transducing↗
PubMed1997

Linear transduction of natural stimuli by dark-adapted and light-adapted rods of the salamander, Ambystoma tigrinum.

1. We examined signal, noise and response properties of salamander rod photoreceptors by measuring: (a) the circulating current of rods which were adapted to darkness and to a wide range of backgrounds; (b) contrasts of natural environments; (c) the effect of adaptation on the linear response range of rods; and (d) the behaviour of rods responding to dynamically modulated stimuli having a range of contrasts found in nature. 2. In the dark, the circulating current contained two noise components analogous to those described in toad. A discrete noise component consisted of events occurring at a rate of 1 event per 32 s (21 degrees C) and had a variance of 0.036 pA2. A continuous noise component contributed 0.022 pA2 to the dark current, roughly equal to the discrete noise variance. 3. Exposure to a wide range of steady backgrounds (suppressing up to 80% of the circulating current), elicited a sustained fluctuating photocurrent having a power spectrum which resembled those of single photon responses and was consistent with the linear summation of single photon events; this indicates that the primary source of noise in the current is caused by the light. 4. Eighty-nine per cent of the contrasts (C) measured in natural environments had magnitude of C < 50%, where C = magnitude of I - Imean/magnitude of Imean. The linear response range elicited by brief flashes expanded with brighter backgrounds, well-encompassing flash contrasts of 100%. 5. Dynamically modulated stimuli and incremental flashes having contrasts similar to those in natural scenes elicited small currents which deviated by a few picoamps about the mean and the transfer functions computed from each type of stimulus-response pair closely corresponded to one another. These results indicate that in natural environments, rods behave as linear small-signal transducers of light.

Adaptation, Ocular↗
PubMed1976

The Roy adaptation model. Using the adaptation model in a practitioner curriculum.

We believe that nurse practitioner role mastery should occur through supplementation of former roles, beginning early and continuing throughout the entire educational process, rather than through realignment to a new role. The educational process should therefore enable the student to identify with and build upon her role as a nurse, rather than abandoning it and adapting to a new quasi-role. If role mastery is to occur by gradual assimilation rather than by abrupt change, a nursing model is needed on which both preparation for and practice in the role can be based. The adaptation model provides the necessary framework to give direction to practitioner education; offers a relevant way of viewing the older adult in relation to his environment; and delineates guidelines for nurse practitioner action.

Adaptation, Physiological↗
PubMed1979

Light adaptation in cone photoreceptors: the occurrence and significance of unitary adaptive strength.

The behavior of "peak response-log intensity" functions generated by the "dark glasses model" is examined and is shown to describe previously observed light adapted behavior in cone photoreceptors. The models of Boynton and Whitten (1970) and Norman and Werblin (1974) are closely related to the dark glasses model--the Boynton-Whitten model being more specific and the Normann-Werblin model more general. For the models, a certain parameter relationship will produce systems which have optimal intensity discriminative capacities. When the data are fitted, this parameter relationship--unitary adaptive strength--seems to emerge. Possible evolutionary and psychophysical implications are discussed.

Adaptation, Ocular↗
PubMed1975

Ion conductance changes associated with spike adaptation in the rapidly adapting stretch receptor of the crayfish.

The time course of the repetitive impulse discharges has been investigated for two high intensities of maintained depolarizing currents, 30 nA and 50 nA, for which the receptor adaptation was complete within 70 msec. The changes in sodium and potassium conductance associated with the decline in spike activity have been analyzed at different instances of time by interrupting in successive experiments the various action potentials in the pulse trains either at the early phase by holding the potential at about -60 mV and recording the inward current (upstroke-gNa) or by evaluating the delayed outward current flowing as the result of a depolarizing voltage pulse which at the end of the action potential re-increased the membrane potential by mV (after potentialgK). At the higher current intensity of 50 nA the discharge frequency was increased, while larger reductions in upstroke-gNa and after potential-gK during receptor adaptation became apparent. The progressive decrease in pulse amplitude from 99 mV to 63 or 55 mV is paralleled by a gradual reduction in upstroke-gNa from 97 mmho/cm-2 to 37 or 27.5 mmho/cm-2 and in after potential-gK from 11.5 mmho/cm-2 to about 7 mmho/cm-2. When under a stimulus of 30 nA the sodium conductance decreases to an average value of 37 mmho/cm-2 only a distorted spike can be elicited, while the spike activity was completely suppressed at upstroke-gNa equals 27.5 mmho/cm-2 was essentially the same under both conditions. The results have been interpreted in terms of the model for impulse generation formulated by Michaelis and Chaplain (1973). According to the model both sodium and potassium inactivation reduce the pulse amplitude. However, while Na-inactivation reduces the frequency of impulse discharge, the K-inactivation actually leads to an increase in spike frequency. As the frequency of the short train of pulses recorded under high-intensity current stimulation remained essentially unaltered, it is suggested that the coupling between Na- and K-inactivation actually leads to an increase in spike frequency. As the frequency of the short train of pulses recorded under high-intensity current stimulation remained essentially unaltered, it is suggested that the coupling between Na- and K-inactivation ensures a constancy of the information-carrying parameter, i.e. the average impulse density.

Action Potentials↗
PubMed2004

Adaptive mutation and amplification in Escherichia coli: two pathways of genome adaptation under stress.

The neo-Darwinists suggested that evolution is constant and gradual, and thus that genetic changes that drive evolution should be too. However, more recent understanding of phenomena called adaptive mutation in microbes indicates that mutation rates can be elevated in response to stress, producing beneficial and other mutations. We review evidence that, in Escherichia coli, two separate mechanisms of stress-induced genetic change occur that revert a lac frameshift allele allowing growth on lactose medium. First, compensatory frameshift ("point") mutations occur by a mechanism that includes DNA double-strand breaks and (we have suggested) their error-prone repair. Point mutation requires induction of the RpoS-dependent general stress response, and the SOS DNA damage response leading to upregulation of the error-prone DNA polymerase DinB (Pol IV), and occurs during a transient limitation of post-replicative mismatch repair activity. A second mechanism, adaptive amplification, entails amplification of the leaky lac allele to 20-50 tandem repeats. These provide sufficient beta-galactosidase activity for growth, thereby apparently deflecting cells from the point mutation pathway. Unlike point mutation, amplification neither occurs in hypermutating cells nor requires SOS or DinB, but like point mutation, amplification requires the RpoS-dependent stress response. Similar processes are being found in other bacterial systems and yeast. Stress-induced genetic changes may underlie much of microbial evolution, pathogenesis and antibiotic resistance, and also cancer formation, progression and drug resistance.

Adaptation, Biological↗
PubMed2005

Validation of a computerized adaptive version of the Schedule for Nonadaptive and Adaptive Personality (SNAP).

This is a validation study of a computerized adaptive (CAT) version of the Schedule for Nonadaptive and Adaptive Personality (SNAP) conducted with 413 undergraduates who completed the SNAP twice, 1 week apart. Participants were assigned randomly to 1 of 4 retest groups: (a) paper-and-pencil (P&P) SNAP, (b) CAT, (c) P&P/CAT, and (d) CAT/P&P. With number of items held constant, computerized administration had little effect on descriptive statistics, rank ordering of scores, reliability, and concurrent validity, but was preferred over P&P administration by most participants. CAT administration yielded somewhat lower precision and validity than P&P administration, but required 36% to 37% fewer items and 58% to 60% less time to complete. These results confirm not only key findings from previous CAT simulation studies of personality measures but extend them for the 1st time to a live assessment setting.

Adaptation, Psychological↗
PubMed1989

Muscle enzyme adaptation in patients with peripheral arterial insufficiency: spontaneous adaptation, effect of different treatments and consequences on walking performance.

1. The activities of phosphofructokinase (PFK), citrate synthetase (CS), lactate dehydrogenase (LDH), 3-hydroxyacyl-CoA dehydrogenase (ACDH) and cytochrome-c oxidase(Cyt-ox) in the calf muscle tissue were compared in subjects with intermittent claudication (n = 38) and controls (n = 20). The activities of CS, ACDH and Cyt-ox were increased and the activity of Cytox was positively correlated to the maximal walking distance (MWD) in the patients. 2. Thirty-three patients with intermittent claudication were randomized to three treatment groups: (1) operative surgery, (2) operative surgery supplemented with physical training and (3) physical training alone. Before and after 6-12 months of treatment, symptom-free walking distance (SFWD), MWD, ankle-brachial blood pressure quotient (ankle index), maximal plethysmographic calf blood flow (MPBF) and the activities of PFK, CS, LDH, ACDH and Cyt-ox were measured. 3. SFWD and MWD increased in all three groups. Ankle index and MPBF increased in groups 1 and 2, but were unchanged in group 3. The activities of Cyt-ox and CS decreased with operation, but the activity of Cyt-ox was further augmented with training in group 3. Overall, the change in ankle index explained 80-90% of the variability in walking performance. In a separate analysis, the increased activity of Cyt-ox in group 3 was positively correlated to, and explained 31% of the variability in, the improvement in SFWD. 4. These findings indicate that both physical activity and a reduced calf blood flow are necessary conditions for the enzymatic adaptation to take place. A causal relationship between metabolic adaptation in the muscle tissue and walking performance is suggested.(ABSTRACT TRUNCATED AT 250 WORDS)

Adaptation, Physiological↗
PubMed1983

Heart rate and QT interval in subjects adapted to beta-blockade: bradycardia and hypotension as uncorrelated adaptations.

Subjects in whom it was found that after a month's treatment with beta-blockers there was a fall of not less than 10 mmHg in systolic blood pressure persisting 54 h after cessation of treatment were considered to have "adapted". Significant falls of blood pressure and heart rate were observed, and were still present after two further weeks of treatment with placebo, but these adaptations were not correlated with each other. Fourteen hypertensive patients and five normotensive subjects received oral propranolol 80 mg, or metoprolol 100 mg, twice daily for 5 days. They were studied before treatment, and 54 h after the last dose. Drug administration was continued for a further 26 days, and the subjects were again examined 54 h after cessation of treatment. Blood was withdrawn at the times of study and contained negligible amounts of drug in the plasma. Records were made of blood pressure and ECG at rest and after exercise, the post-exercise QT being measured at a heart rate of exactly 100 beats per minute, obviating the need for any correction of QT. QT intervals were significantly prolonged, both at rest and on exercise. Responses to intravenous propranolol 10 mg or metoprolol 20 mg were also measured during the study periods, and no hypersensitivity to the drugs was found at rest or after exercise.

Adaptation, Physiological↗
PubMed1991

Expression of cell cycle related proteins--proliferating cell nuclear antigen (PCNA) and statin--during adaptation and de-adaptation of EUE cells to a hypertonic medium.

EUE cells adapted to grow for long times in a hypertonic medium have a longer cell cycle than those growing in isotonic medium. To elucidate whether this lengthening involves specific cycle phases to differing extents, the expression of two cycle-related protein, PCNA and statin, was studied by dual parameter flow cytometry of indirect immunofluorescence protein labelling and DNA content. In isotonic medium, most cells, in all the cycle phases, were PCNA positive; in contrast, PCNA negative cells and statin positive cells were very few in number and only fell in the G0/1 range of DNA contents. In hypertonic medium, the frequency of PCNA positive cells was lower, and that of statin positive cells higher, than in isotonic medium, particularly in the G0/1 range of DNA contents: this suggests that a G0 block occurs under long-term hypertonic stress. Consistently, dual parameter flow cytometric measurement of BrdUrd immunofluorescence labelling and DNA content showed that fewer cells entered S phase in hypertonic medium and their progression through the S phase was slower; evidence was also found for the occurrence of a G2 block. These kinetics changes were fully reversible in isotonic medium, thus indicating the adaptive nature of the EUE response to hypertonicity.

Adaptation, Physiological↗
PubMed2006

Physiological adaptation in early human pregnancy: adaptation to balance maternal-fetal demands.

After conception, the corpus luteum, placenta, and developing embryo release hormones, growth factors, and other substances into the maternal circulation. These substances trigger a cascade of events that transform the functioning of the maternal cardiovascular, respiratory, and renal systems, which in turn alter the physicochemical determinants of [H(+)]. Following implantation, maternal adaptations fulfill 4 important functions that support fetal growth. Increased availability of substrates and precursors for fetal-placental metabolism and hormone production is mediated by increases in dietary intake, as well as endocrine changes that increase the availability of glucose and low-density lipoprotein (LDL) cholesterol. Transport capacity is enhanced by increases in cardiac output, facilitating the transport of substrates and precursors to the placenta, and fetal waste products to maternal organs for disposal. Maternal-fetal exchange is regulated by the placenta after 10-12 weeks gestation, but it may occur through histiotrophic mechanisms before this time. Disposal of additional waste products (heat, carbon dioxide, and metabolic byproducts) occurs through peripheral vasodilation and increases in skin blood flow, ventilation, and renal filtration. The maternal physiological adaptations described above must meet the combined demands of maternal exercise and fetal growth. More research is needed to formulate evidence-based guidelines for healthy physical activity in early pregnancy.

Adaptation, Physiological↗
PubMed2001

Structural adaptation of microvascular networks: functional roles of adaptive responses.

Terminal vascular beds continually adapt to changing demands. A theoretical model is used to simulate structural diameter changes in response to hemodynamic and metabolic stimuli in microvascular networks. Increased wall shear stress and decreased intravascular pressure are assumed to stimulate diameter increase. Intravascular partial pressure of oxygen (PO(2)) is estimated for each segment. Decreasing PO(2) is assumed to generate a metabolic stimulus for diameter increase, which acts locally, upstream via conduction along vessel walls, and downstream via metabolite convection. By adjusting the sensitivities to these stimuli, good agreement is achieved between predicted network characteristics and experimental data from microvascular networks in rat mesentery. Reduced pressure sensitivity leads to increased capillary pressure with reduced viscous energy dissipation and little change in tissue oxygenation. Dissipation decreases strongly with decreased metabolic response. Below a threshold level of metabolic response flow shifts to shorter pathways through the network, and oxygen supply efficiency decreases sharply. In summary, the distribution of vessel diameters generated by the simulated adaptive process allows the network to meet the functional demands of tissue while avoiding excessive viscous energy dissipation.

Adaptation, Physiological↗