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PubMed1975

Effect of activation and adaptation on the sensitivity of slowly adapting cutaneous mechanoreceptors.

The effect of adaptation on the sensitivity of type I and type II cutaneous mechanoreceptors was evaluated with test stimuli applied before, during and after a persistent indentation (offset) of the skin. It was found that the offset initially lowered the threshold to both high (100-200 Hz) and low (1-20 Hz) frequency sinusoidal stimuli, as compared with the preoffset condition. This lowered threshold increased for both stimuli as adaptation progressed. When adaptation was nearly complete, there was an appreciable residual reduction of threshold, as compared with preoffset values, for the low frequency stimuli but not for high frequency stimuli. For a time after the offset was removed, the threshold was increased above preoffset levels for both stimuli. Suprathreshold ramp displacements superimposed on an offset caused higher maximal frequencies and a larger change in frequency than before the offset was applied. This difference often was considerable (20-40 impulses/sec) even though the discharge produced by the offset had adapted to only 2-4 impulses/sec above the preoffset level. Shortly after removal of the offset, the ramp responses typically were less than before the offset was applied. Thus, these receptors are not "reset" to the preoffset condition by adaptation nor is their sensitivity reduced. On the contrary, they respond more vigorously to superimposed stimuli except for near threshold displacements that are brief and rapid.

Adaptation, Physiological↗
PubMed1995

Adaptation mechanisms in spatial vision--II. Flash thresholds and background adaptation.

To examine how the mechanisms of light adaptation affect spatial pattern vision, contrast detection thresholds were measured for sinusoidal (increment-Gabor) probes on flashed backgrounds in the presence of steady adapting backgrounds. The thresholds for all spatial frequencies (1-12 c/deg), flashed-background intensities (dark to 4 log td) and adapting-background intensities (dark to 4 log td) were adequately described by a simple model consisting of a compressive nonlinearity (a modified Naka-Rushton function), a subtractive adaptation factor, and a multiplicative adaptation factor. For all five subjects the compressive nonlinearity was found to vary systematically with spatial frequency; for all but one subject, the subtractive and multiplicative factors were found to be relatively constant.

Adaptation, Ocular↗
PubMed1995

Adaptive determinism during salt-adaptation in Sorghum bicolr.

During adaptation to salinity, plants of Sorghum bicolor showed malformations affecting the leaves in development (DPL). At the end of the adaptation process, the plants were regrouped according to their pattern of DPL response. The distribution of the plant population in different patterns depended on environmental conditions. However, a positive relationship between the frequency of a pattern and its rate of development has been found. Similarly, a negative relation between the frequency of a pattern and the rate of senescence for the same pattern has been observed. The results reveal the existence of an orientation of the plant response towards the patterns with highest developmental rate and lowest rate of senescence. This property is defined as 'adaptive determinism'. Results indicate that the NaCl acts as a trigger for adaptation to a whole range of environmental perturbations. This suggests that adaptation to salinity is not a pre-programed response of the plants, and may be related to learning processes occurring in animals.

Adaptation, Physiological↗
PubMed1994

A comparison of the second harmonic generation from light-adapted, dark-adapted, blue, and acid purple membrane.

The second order nonlinear polarizability and dipole moment changes upon light excitation of light-adapted bacteriorhodopsin (BR), dark-adapted BR, blue membrane, and acid purple membrane have been measured by second harmonic generation. Our results indicate that the dipole moment changes of the retinal chromophore, delta mu, are very sensitive to both the chromophore structure and protein/chromophore interactions. Delta mu of light-adapted BR is larger than that of dark-adapted BR. The acid-induced formation of the blue membrane results in an increase in the delta mu value, and formation of acid purple membrane, resulting from further reduction of pH to 0, returns the delta mu to that of light-adapted BR. The implications of these findings are discussed.

Adaptation, Physiological↗
PubMed2002

The balance between adaptability and adaptation.

In his 1983 book, Adaptability, Michael Conrad explored the quantitative relationship between adaptability and adaptation using the conditional 'entropy' of information theory as his primary tool. The conditional entropy can be used to estimate the connectivity of the network of system exchanges, a key indicator of system stability. In fact, the May-Wigner criterion for the stability of linear dynamical systems can be recast using the conditional entropy to help identify the boundary along which adaptability and adaptation are exactly in balance-the 'edge of chaos' as it is popularly known. Real data on networks of ecosystem flows indicate that in general these systems do not exist nigh upon the edge of chaos, but rather they populate a much wider 'window of vitality' that exists between the realms of chaotic and deterministic dynamics. It appears that the magnitudes of network flows within this region are distributed in power law fashion. The theory also suggests that an absolute limit to the connectivity of natural self-organizing systems exists, at approximately 3.015 effective connections per node.

Adaptation, Physiological↗
PubMed2003

Protein adaptations to temperature and pressure: complementary roles of adaptive changes in amino acid sequence and internal milieu.

Retention of required structural and functional properties of proteins in species adapted to different temperatures and pressures is achieved through variation in amino acid sequence and accumulation of small organic solutes that stabilize protein traits. Conservation of ligand binding and catalytic rate can be achieved by minor differences in sequence. For orthologs of lactate dehydrogenase-A (A(4)-LDH) temperature adaptation may involve only a single amino acid substitution. Adaptation involves changes in conformational mobility of regions of A(4)-LDH that undergo movement during ligand binding, movements that are rate-limiting to catalysis. A model that integrates adaptations in sequence and intracellular milieu is developed on the basis of conformational microstates. Although orthologs of different thermally adapted species vary in stability, at physiological temperatures it is hypothesized that a similar ensemble of conformational microstates exists for all orthologs. Organic solutes stabilize this ensemble of microstates. Differences among orthologs in responses to organic solutes at a common temperature lead to similar responses at normal body temperatures. Because protein stability increases at high protein concentrations, intrinsic stabilities of proteins may reflect the protein concentrations of the cellular compartments in which they occur. Protein-stabilizing solutes like trimethylamine-N-oxide (TMAO) conserve protein function and structure at elevated hydrostatic pressures.

Adaptation, Physiological↗
PubMedDate not supplied

An adaptive Reichardt detector model of motion adaptation in insects and mammals.

There are marked similarities in the adaptation to motion observed in wide-field directional neurons found in the mammalian nucleus of the optic tract and cells in the insect lobula plate. However, while the form and time scale of adaptation is comparable in the two systems, there is a difference in the directional properties of the effect. A model based on the Reichardt detector is proposed to describe adaptation in mammals and insects, with only minor modifications required to account for the differences in directionality. Temporal-frequency response functions of the neurons and the model are shifted laterally and compressed by motion adaptation. The lateral shift enhances dynamic range and differential motion sensitivity. The compression is not caused by fatigue, but is an intrinsic property of the adaptive process resulting from interdependence of temporal-frequency tuning and gain in the temporal filters of the motion detectors.

Adaptation, Physiological↗
PubMed2003

Presence of long-lasting peripheral adaptation in oblique-banded leafroller, Choristoneura rosaceana and absence of such adaptation in redbanded leafroller, Argyrotaenia velutinana.

Pre-exposure of male oblique-banded leafrollers, Choristoneura rosaceana (Harris), to the main component of their pheromone blend and traces of its geometric isomer (Z11-14:Ac and E11-14:Ac, respectively) at 36 +/- 12 ng/ml air for durations of 15 and 60 min in sealed Teflon chambers with continuous air exchange significantly reduced peripheral sensory responses to these compounds as measured by electroantennograms (EAGs). The EAG responses of C. rosaceana to all tested dosages of pheromonal stimuli and blank controls were lowered by 55-58% and made a linear recovery to 70-100% of the pre-exposure amplitude within 12.5 min at a rate of 3-4 %/min. Exposures of 5 min were insufficient to maximally adapt C. rosaceana; however, exposures of 15 and 60 min reduced sensory responsiveness to the same minimum. In contrast, EAG responses of redbanded leafroller, Argyrotaenia velutinana (Walker), after identical pheromone exposure for 5 and 60 min yielded no long-lasting peripheral sensory adaptation as measured by EAGs, even though this species shares the same main pheromone components with C. rosaceana. We postulate that the long-lasting peripheral adaptation observed for C. rosaceana is a mechanism that impedes central nervous system habituation in this species. In contrast, A. velutinana may be more susceptible to central nervous system habituation because it lacks the capacity for minutes-long adaptation. We propose that long-lasting adaptation may be a mechanism explaining some of the variation in efficacy of pheromone-based mating disruption across taxa.

Adaptation, Physiological↗
PubMed1999

Tolerance of acid-adapted and non-adapted Escherichia coli O157:H7 cells to reduced pH as affected by type of acidulant.

A study was carried out to determine if three strains of Escherichia coli O157:H7 grown (18 h) in Tryptic Soy Broth (TSB) and TSB supplemented with 1.25% glucose (TSBG), i.e. unadapted and acid-adapted cells, respectively, exhibited changes in tolerance to reduced pH when plated on Tryptic Soy Agar (TSA) acidified (pH 3.9, 4.2, 4.5, 4.8, 5.1 and 5.4) with acetic, citric or malic acids. All test strains grew well on TSA acidified with acetic acid at pH > or = 5.4 or malic acid at pH > or = 4.5; two strains grew on TSA acidified with citric acid at pH > or = 4.5, while the third strain grew at pH > or = 4.8. Acid-adapted and control (unadapted) cells differed little in their ability to form visible colonies on TSA containing the same acid at the same pH. However, on plates not showing visible colonies, acid-adapted cells retained higher viability than unadapted cells when plated on acidified TSA. Growth of acid-adapted and control cells of E. coli O157:H7 inoculated into TSB containing acetic acid (pH 5.4 and 5.7) and citric or malic acids (pH 4.2 and 4.5) was also studied. There was essentially no difference in growth characteristics of the two types of cells in TSB acidified at the same pH with a given acid. Tolerance of acid-adapted and control cells on subsequent exposure to low pH is influenced by the type of acidulant. The order of sensitivity at a given pH is acetic > citric > malic acid. When performing acid challenge studies to determine survival and growth characteristics of E. coli O157:H7 in foods, consideration should be given to the type of acid to which cells have been exposed previously, the procedure used to achieve acidic environments and possible differences in response among strains. The use of strains less affected by pH than type of acidulant or vice versa could result in an underestimation of the potential for survival and growth of E. coli O157:H7 in acid foods.

Acids, Acyclic↗
PubMed1979

The surface epithelium of teleostean fish gills. Cellular and junctional adaptations of the chloride cell in relation to salt adaptation.

Various species of teleostean fishes were adapted to fresh or salt water and their gill surface epithelium was examined using several techniques of electron microscopy. In both fresh and salt water the branchial epithelium is mostly covered by flat respiratory cells. They are characterized by unusual outer membrane fracture faces containing intramembranous particles and pits in various stages of ordered aggregation. Freeze fracture studies showed that the tight junctions between respiratory cells are made of several interconnecting strands, probably representing high resistance junctions. The organization of intramembranous elements and the morphological characteristics of the junctions do not vary in relation to the external salinity. Towards the base of the secondary gill lamellae, the layer of respiratory cells is interrupted by mitochondria-rich cells ("chloride cells"), also linked to respiratory cells by multistranded junctions. There is a fundamental reorganization of the chloride cells associated with salt water adaptation. In salt water young adjacent chloride cells send interdigitations into preexisting chloride cells. The apex of the seawater chloride cell is therefore part of a mosaic of sister cells linked to surrounding respiratory cells by multistranded junctions. The chloride cells are linked to each other by shallow junctions made of only one strand and permeable to lanthanum. It is therefore suggested that salt water adaptation triggers a cellular reorganization of the epithelium in such a way that leaky junctions (a low resistance pathway) appear at the apex of the chloride cells. Chloride cells are characterized by an extensive tubular reticulum which is an extension of the basolateral plasma membrane. It is made of repeating units and is the site of numerous ion pumps. The presence of shallow junctions in sea water-adapted fish makes it possible for the reticulum to contact the external milieu. In contrast in the freshwater-adapted fish the chloride cell's tubular reticulum is separated by deep apical junctions from the external environment. Based on these observations we discuss how solutes could transfer across the epithelium.

Adaptation, Physiological↗
PubMed1996

Mouth movements diminish taste adaptation, but rate of mouth movement does not affect adaptation.

The degree of adaptation to five concentrations of sucrose was measured. Solutions were kept in the mouth for 25 s; a sweetness judgement was given every 5 s. There were four conditions of mouth movements: no movement, slow, medium and fast mouth movements. It was found that when mouth movements are made there is less adaptation than when there is no mouth movement; however, the rate of movement does not appear to influence the degree of adaptation. Furthermore concentration was found to have an effect. In the no-movement condition, the degree of adaptation seems to rise with concentration, whereas in the movement conditions the opposite effect occurs, i.e. a decrease in the degree of adaptation occurs with increasing sucrose concentration. These phenomena might be explained by the stimulated tongue area, or by taste constancy.

Adaptation, Physiological↗
PubMed1993

Mechanism of baroreceptor adaptation in dogs: attenuation of adaptation by the K+ channel blocker 4-aminopyridine.

1. Increased arterial pressure increases baroreceptor activity but activity declines (i.e. baroreceptors adapt) as the pressure is maintained at the higher level. The purpose of this study was to investigate the role of a 4-aminopyridine (4-AP)-sensitive K+ current in causing baroreceptor adaptation. 2. Multi- and single fibre recordings of baroreceptor activity were obtained from the vascularly isolated carotid sinus in anaesthetized dogs during step increases in carotid sinus pressure sustained for periods up to 5 min. 3. Baroreceptor activity increased with the rise in pressure, declined markedly over the first minute, and continued to decline at a slower rate during the remainder of the 5 min period of elevated pressure. Exposure of the isolated carotid sinus to 4-AP (10(-5) and 10(-4) M) attenuated adaptation in a dose-dependent and reversible manner (P < 0.05). 4-AP attenuated the gradual decline in single fibre activity and also prevented derecruitment or dropout of fibres that occurred over time. 4-AP did not alter peak nerve activity measured within the first 2 s of the pressure step. 4. Ouabain (5 x 10(-7)-10(-6) M), an inhibitor of Na+,K(+)-ATPase, increased baroreceptor activity but did not attenuate baroreceptor adaptation. 5. Neither 4-AP nor ouabain altered the distensibility of the carotid sinus as measured with sonomicrometer crystals suggesting that the agents act directly on the nerve endings. 6. The results suggest that activation of a 4-AP-sensitive K+ current contributes significantly to baroreceptor adaptation with little or no contribution of Na+,K(+)-ATPase.

4-Aminopyridine↗
PubMed2002

Invited review: molecular adaptations in mammalian hibernators: unique adaptations or generalized responses?

Hibernators are unique among mammals in their ability to attain, withstand, and reverse low body temperatures. Hibernators repeatedly cycle between body temperatures near zero during torpor and 37 degrees C during euthermy. How do these mammals maintain cardiac function, cell integrity, blood fluidity, and energetic balance during their prolonged periods at low body temperature and avoid damage when they rewarm? Hibernation is often considered an example of a unique adaptation for low-temperature function in mammals. Although such adaptation is apparent at the level of whole animal physiology, it is surprisingly difficult to demonstrate clear examples of adaptations at the cellular and biochemical levels that improve function in the cold and are unique to hibernators. Instead of adaptation for improved function in the cold, the key molecular adaptations of hibernation may be to exploit the cold to depress most aspects of biochemical function and then rewarm without damage to restore optimal function of all systems. These capabilities are likely due to novel regulation of biochemical pathways shared by all mammals, including humans.

Adaptation, Physiological↗
PubMed1977

Specific and general contour adaptation effects found using a selective adaptation paradigm.

There is evidence for discrete property analyzers in mammalian visual systems. Research has indicated that prolonged stimulation of such units reduces their sensitivity to subsequent stimulation. Psychophysical studies have employed this effect, terned selective adaptation, to study feature extractors in the human visual system. The purpose of this study was to determine the role of density and deviation in the adaptation figure on the recognition thresholds of simple and complex text figures. A selective adaptation paradigm was employed. A strict property analyzer model suggests that increases in density, deviation, or complexity should lead to an increased recognition time for the test figures. This was not confirmed. The complexity of the test figure had no effect on its recognition time. Both increased density and deviation did have an effect on the recognition times of the test figures. The results thus suggest that contour adaptation involves at least two processes: a general, probably peripheral effect due to the fatigue of visual receptor units and a more specific effect generated by the similarity between test figure and adaptation contours, independent of the site of stimulation.

Adaptation, Ocular↗
PubMed2000

Adaptations made by rheumatoid arthritis patients to continue working: a pilot study of workplace challenges and successful adaptations.

OBJECTIVES: The goals of this pilot study were to use qualitative research techniques in a group of currently employed patients with rheumatoid arthritis (RA) to develop categories of challenges encountered in maintaining employment and categories of successful adaptations made to continue working; and to identify obstacles considered to be persistent threats to continued employment. METHODS: Patients were interviewed by telephone with a questionnaire composed of structured-response format and open-ended response format questions focusing on specific challenges and adaptations in the workplace. RESULTS: Of the 22 patients interviewed, 96% were women, mean age was 50 years, 84% were college graduates, and the majority had light physical job demands and high autonomy over their work and hours worked. Patients encountered diverse challenges, such as fatigue, pain, typing, writing, physical requirements, maintaining a pleasant disposition, working overtime, traveling for business, commuting, being on time, not being able to choose rest periods, and environmental issues. Patients also made multiple adaptations to continue working, the most helpful being changing job or altering career path (36%), altering work hours (32%), using more disease-modifying antirheumatic drugs (27%), using car service (23%), sleeping more (18%), and working at home (14%). Patients were not at all confident in their ability to continue working because of RA, and perceived the following persistent threats to continued employment: fatigue (45%), not being able to use hands (45%), not being able to choose rest periods (27%), and commuting problems (18%). In addition, patients confronted psychological stresses, such as dealing with coworkers and supervisors and balancing job and personal roles. These challenges and adaptations included unfavorable work-related occurrences, or "negative work-role events." CONCLUSIONS: Seemingly successfully employed patients with RA faced multiple challenges and made major adaptations to maintain employment and still perceived their employment to be in jeopardy because of RA. The findings of this study have important implications for screening patients at risk for negative work-role events and for possible work-related and social support interventions aimed at preserving employment.

Activities of Daily Living↗
PubMed1979

[Dynamic behavior of the adaptive control system, hypothalamus--anterior pituitary--adrenal cortex. Animal experimental study of the adequate system dynamics of the direct and indirect parameters of the adaptive control system].

The dynamic response of the adaptive closed-loop control system hypothalamus-anterior pituitary-adrenal cortex after application of short-time disturb pulses were examined experimentally in the pig. Blood sampling was performed biologically non-reactive by chronically implanted vascular catheters in the upper vena cava. A circadian biphase periodical dynamics characterizes the distrubance response of the adaptive control system, respectively, its direct and indirect parameters. After distrubance variables induced initial excess the plasma corticosteriods undershoot the basic level over a long period. Conversely, the dynamics of the eosinophils is determined through an initial eosinopenic phase and a subsequent typical overshoot. Periodical dynamic is absent in the steady state. The controller of the adaptive system does not show any spontaneous activity in the steady state without stress. The absence of an endogenic periodicity of the dependent parameters likewise gives evidence of an active oscillator. On the other hand, the controlling unit of the adaptive system constitutes a control response of circadian periodicty after activation by disturbance variables in pulse shape. The high damping of the control system terminates the transient state within 24 hours, and the corticosteriods and the eosinophils reach the steady state level. This control quality of the adaptive control system gains a high importance in the origination of the spontaneous circadian periodicity by corticosteriods and eosinophils and for the biological compensation of exogenous distrubance variables.

11-Hydroxycorticosteroids↗
PubMed1989

[Study on choroidal blood flow at dark and light adaptation. 1. Choroidal blood flow at dark adaptation].

The effect of dark adaptation on choroidal blood flow (CBF) was studied in albino rabbits. CBF was measured by the hydrogen clearance method. There was no significant change of CBF at dark adaptation in both short term dark adaptation, in which CBF had been expected to increase due to increased oxygen demand of the outer retina, and long term dark adaptation, in which CBF had been expected to decrease due to depressed function of visual cells and retinal pigment epithelium. The results show that dark adaptation does not influence CBF, in spite of the close relationship between the outer retina and the choroidal circulation. The large blood flow of the choroidal circulation may not need the reaction mechanism for the functional changes of the outer retina.

Animals↗
PubMed1994

[Adaptive and non-adaptive reactions of vision in the Far North].

The paper deals with the study of specific features of ocular adaptive reactions under the conditions of the Far North. The author suggests that there should be 3 types of ocular adaptation in the North: (1) and (2) being at the individual level and (3) at the population level. Type 1 adaptation is usually observed within the first months of stay in the North. The ocular status of newcomers is characterized by lower hydrodynamic parameters: a tendency to intraocular vascular dystonia (the hypertensive type) is formed. Type 2 adaptation is generally seen after spending 10 years of stay in the North. Persistent physiological vascular reactions are formed (within the upper normal range). Organic disadaptive changes in microvasculature develop in a third of the new residents in the North. Type 3 hereditary long-term adaptation is observed in the indigenous residents of the North. The most optimum ratios of hemo- and hydrodynamic parameters along with definite changes in anatomic and functional indices form in them, which is reflected in the specific features of eye diseases.

Adaptation, Ocular↗