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At least 127 records · Page 7Linked to original sources

PubMed1996

Adaptation to repeated restraint stress in rats: failure of ethanol-treated rats to adapt in the stress schedule.

Adaptation to a repeated restraint stress schedule was monitored in ethanol-treated and control rats. A single episode of 2 h restraint decreased food intake in both control and ethanol-treated rats. The decreases in control rats were not observed following the 5th daily restraint of 2 h/day, suggesting that adaptation has occurred. Ethanol-treated rats, however, exhibited decreased food intake even after 5th daily restraint of 2 h/day. Ethanol administration decreased weekly but not daily cumulative food intake in unrestrained rats. Food intakes of ethanol-treated and control restrained rats were comparable following 1st-3rd daily restraints, but were smaller in ethanol-treated rats following the 4th and 5th daily restraints. Open-field ambulatory activities monitored 24 h after the 5th daily restraint on the 6th day were comparable in control restrained and unrestrained rats. Ethanol-treated and control unrestrained rats also exhibited comparable ambulation, but ethanol-treated rats exhibited smaller activity than control restrained or ethanol-treated unrestrained rats. Fluid intakes of ethanol and control rats were comparable during the 2 weeks of ethanol administration, but daily restraint schedule decreased ethanol intake. The findings show adaptation to repeated restraint in control rats and inability of ethanol-treated rats to adapt in the stress schedule. These findings imply that excessive alcohol consumption may impair adaptation to stress and thus conceivably precipitate depression.

Alcoholism↗

PubMed2001

Evolution of adaptive synapses: robots with fast adaptive behavior in new environments.

This paper is concerned with adaptation capabilities of evolved neural controllers. We propose to evolve mechanisms for parameter self-organization instead of evolving the parameters themselves. The method consists of encoding a set of local adaptation rules that synapses follow while the robot freely moves in the environment. In the experiments presented here, the performance of the robot is measured in environments that are different in significant ways from those used during evolution. The results show that evolutionary adaptive controllers solve the task much faster and better than evolutionary standard fixed-weight controllers, that the method scales up well to large architectures, and that evolutionary adaptive controllers can adapt to environmental changes that involve new sensory characteristics (including transfer from simulation to reality and across different robotic platforms) and new spatial relationships.

Computer Simulation↗

PubMed1978

[Na-K ionic pump and spike adaptation in the slowly and rapidly adapting stretch receptor neuron of the crayfish Orconectes limosus (RAF.)].

A very important cause of the spike adaptation in the slowly adapting stretch receptor neuron (SN1) is the Na-K ionic pump. An increasing inhibition of the ionic pump, produced by gradual reduction of the external K+-concentration or application of rising doses of ouabain, is correlated with an adequate diminution of frequency decay. But even high concentrations of ouabain (10(-3) -- 5 . 10(-3) M) can not completely abolish the spike adaptation. Immediately after the onset of a current step the impulse frequency still declines. In agreement with these findings the gain in the Bode diagram shows a maximum further on. The spike adaptation in the rapidly adapting neuron (SN2) can only in a smaller part be attributed to the action of the ionic pump. Application of ouabain causes in the SN2, contrary to SN1, only a low depolarization of the membrane potential. The decay of impulse frequency is considerably diminished but a long lasting nearly stationary discharge like in the SN1 can never be observed.

Animals↗

PubMed1997

Evolutionary psychology and genetic variation: non-adaptive, fitness-related and adaptive.

Behavioural variation across individuals can be substantial. A broad generalization emerging from three decades of behavioural genetic studies is that most psychological individual differences have moderate broad heritabilities (30-60%). There are at least three possible scenarios for this genetic variation. First, it may be adaptively neutral and not subject to selection. Second, it may be related to fitness despite selection. Third, it may be maintained by selection for alternative adaptations. Some authors favour the first of these possibilities, but the latter two cannot be ruled out. First, temporally varying selection pressures (e.g. pathogens) can maintain fitness-related genetic variance in a population despite current selection pressures. Moreover, direct and indirect evidence on humans support the notion that some phenotypic variance is fitness related. Second, while adaptive alternatives are unlikely to be found at a level of highly complex design, frequency dependent selection can maintain variation at finer, quantitative levels. One potential example is discussed. Because of their particular relevance to evolutionary psychology, fitness-related and adaptive genetic variance deserve further attention.

Adaptation, Psychological↗

PubMed1987

Two types of chloride cells in the gill epithelium of a freshwater-adapted euryhaline fish: Lebistes reticulatus; their modifications during adaptation to saltwater.

Two types of chloride cells were identified in the gill epithelium of freshwater-adapted guppies. One type, referred to as an "alpha-chloride cell," was a pale, elongated cell located at the base of the secondary lamella in close contact with the arterioarterial pillar capillaries. In its cytoplasm, membranous tubules in continuity with its basolateral plasma membrane formed an extended tridimensional network. The vesiculotubular system (Pisam: Anat. Rec. 200:401-414, 1981) consisted of a few tubules and vesicles located next to the apical plasma membrane. A second type, referred to as a "beta-chloride cell," was a darker, ovoid cell located in the interlamellar region of the primary epithelium facing the central venous sinus. Membranous tubules in continuity with the basolateral plasma membrane were unevenly distributed in the cytoplasm. A prominent vesiculotubular system composed of numerous vesicles and tubules was found between the Golgi apparatus and the apical surface. During seawater adaptation, the alpha-chloride cells increased in size and progressively transformed into characteristic "seawater alpha-chloride cells" with a well-developed, regular, tight tubular network and numerous vesicles and tubules of the vesiculotubular system accumulated below the apical pit. The beta-chloride cells underwent a progressive degeneration and disappeared. Thus, in freshwater-adapted guppies, there are two types of chloride cells, alpha and beta, respectively, related to the arterial and the venous vessels, whereas in seawater-adapted fishes, a single type of cell, the alpha-chloride cell, was related to both the arterial and venous channels.

Adaptation, Physiological↗

PubMed2006

Is increased maternal basking an adaptation or a pre-adaptation to viviparity in lizards?

Pregnant females modify their thermoregulatory behaviour in many species of viviparous (live-bearing) reptiles, typically maintaining higher and more stable body temperatures at this time. Such modifications often have been interpreted as adaptations to viviparity, functioning to accelerate embryonic development and/or modify phenotypic traits of hatchlings. An alternative possibility is that similar maternal thermophily may be widespread also in oviparous species and if so, would be a pre-adaptation (rather than an adaptation) to viviparity. Because eggs are retained in utero for a significant proportion of development even in oviparous reptiles, maternal thermophily might confer similar advantages in oviparous as in viviparous taxa. Experimental trials on montane oviparous scincid lizards (Bassiana duperreyi) support the pre-adaptation hypothesis. First, captive females (both reproductive and non-reproductive) selected higher temperatures than males. Second, experimentally imposing thermal regimes on pregnant females significantly affected their oviposition dates and the phenotypic traits (body shape, running speed) of their hatchlings. Thus, as for many other behavioural correlates of pregnancy in viviparous reptiles, maternal thermophily likely may have already been present in the ancestral oviparous taxa that gave rise to present-day viviparous forms.

Adaptation, Physiological↗

PubMedDate not supplied

Adaptive designs for pivotal trials: discussion points from the PSI Adaptive Design Expert Group.

The Committee for Medicinal Products for Human Use (CHMP) is currently preparing a guideline on 'methodological issues in confirmatory clinical trials with flexible design and analysis plan'. PSI (Statisticians in the Pharmaceutical Industry) sponsored a meeting of pharmaceutical statisticians with an interest in the area to share experiences and identify potential opportunities for adaptive designs in late-phase clinical drug development. This article outlines the issues raised, resulting discussions and consensus views reached. Adaptive designs have potential utility in late-phase clinical development. Sample size re-estimation seems to be valuable and widely accepted, but should be made independent of the observed treatment effect where possible. Where unblinding is necessary, careful consideration needs to be given to preserving the integrity of the trial. An area where adaptive designs can be particularly beneficial is to allow dose selection in pivotal trials via adding/dropping treatment arms; for example, combining phase II and III of the drug development program. The more adaptations made during a late-phase clinical trial, the less likely that the clinical trial would be considered as a confirmatory trial. In all cases it would be advisable to consult with regulatory agencies at the protocol design stage. All involved should remain open to scientifically valid opportunities to improve drug development.

Clinical Trials as Topic↗

PubMed1987

Dependence of cat vestibulo-ocular reflex direction adaptation on animal orientation during adaptation and rotation in darkness.

Four series of experiments investigated how adaptive changes in direction of the cat's vestibulo-ocular reflex (VOR) vary with position of the animal during adaptive training and postadaptive testing. In all experiments VOR was measured electrooculographically during rotations about earth-horizontal and vertical axes in the dark before and after 2 h of adaptation in which 0.25 Hz sinusoidal whole body rotation about a horizontal/vertical axis was paired with synchronous 0.25 Hz rotation of a visual pattern about a vertical/horizontal axis, respectively. In upright sagittal (US) experiments, coupling of pitch rotation with visual pattern rotation about an earth vertical axis yielded an adaptive horizontal VOR response to pitch rotation whose gain had a local maximum at 0.25-0.5 Hz plus a sustained rise for frequencies below 0.1 Hz. When post-tests were done with the animal rolled 90 degrees onto its side and rotated about the earth vertical axis (pitch relative to the cat), the low frequency rise was eliminated and the 0.25 Hz peak was reduced. In on side sagittal (SS) experiments, where training was done in the latter (on side) position, training produced only the 0.25 Hz peak without the low frequency rise, indicating that the rise is due to coupling of otolith input to horizontal VOR. Again the 0.25 Hz peak was reduced when testing was done with the cat oriented 90 degrees from the training position (in the US position). This indicates that the cross-coupled canal-ocular reflex response is modulated or gated by the position of the animal with respect to gravity.(ABSTRACT TRUNCATED AT 250 WORDS)

Adaptation, Ocular↗

PubMed1987

Effects of adaptation and cross-adaptation to common ions on sourness intensity.

The effects of self and cross-adaptation of acetic acid and HCl solutions on the perception of sourness, were investigated using a filter paper method. In contrast to acetic acid and to pH-buffered acetic acid solutions, self-adaptation could not be obtained with HCl. In fact the sourness of the HCl test-stimulus after adaptation to HCl was increased compared to the sourness obtained with the unadapted tongue. Such a sourness potentiation was also observed with acetic acid and buffered acetic acid solutions after adaptation to distilled water. The results suggest that the reception process eliciting the sour taste of H+ ions and of undissociated acids are different and probably independent.

Acetates↗

PubMed2004

Biological adaptive control model: a mechanical analogue of multi-factorial bone density adaptation.

The mechanism of how bone adapts to every day demands needs to be better understood to gain insight into situations in which the musculoskeletal system is perturbed. This paper offers a novel multi-factorial mathematical model of bone density adaptation which combines previous single-factor models in a single adaptation system as a means of gaining this insight. Unique aspects of the model include provision for interaction between factors and an estimation of the relative contribution of each factor. This interacting system is considered analogous to a Newtonian mechanical system and the governing response equation is derived as a linear version of the adaptation process. The transient solution to sudden environmental change is found to be exponential or oscillatory depending on the balance between cellular activation and deactivation frequencies.

Adaptation, Physiological↗

PubMed2003

Failure to adapt or adaptations that fail: contrasting models on procedures and safety.

This paper introduces two models on procedures and safety and assesses the practical consequences these have for organizations trying to make progress on safety through procedures. The application of procedures is contrasted as rote rule following versus substantive cognitive activity. It reveals a fundamental double bind: operators can fail to adapt procedures when adapting proved necessary, or attempt procedural adaptations that may fail. Rather than simply increasing pressure to comply, organizations should invest in their understanding of the gap between procedures and practice, and help develop operators' skill at adapting.

Adaptation, Psychological↗

PubMed1997

A uniform strain criterion for trabecular bone adaptation: do continuum-level strain gradients drive adaptation?

In this paper, it is postulated that the apparent density of trabecular bone adapts so that continuum-level strains within the bone are uniform and, as a consequence, spatial strain gradients within the bone/marrow continuum are minimized. The feasibility of a uniform strain criterion was tested using computational finite-element analysis of the proximal femur. We demonstrated that (1) this criterion produced a realistic apparent density distribution in the proximal femur, (2) the solutions for apparent density were convergent and unique, (3) predicted apparent densities compared well to experimental measurements, and (4) strain gradients within the bone/marrow continuum were reduced substantially. Thus, a possible goal of trabecular bone adaptation may be the reduction of strain gradients within the bone/marrow continuum. Osteocytes within the bone tissue and bone cells on the surface of a trabeculum are mechanosensitive and play a role in bone adaptation. In addition, the bone marrow is rich in osteoprogenitor cells near the bone surface that are mechanosensitive. Strain gradients within bone/marrow continuum cause pressure gradients in the marrow, causing extracellular fluid flow which could stimulate osteoprogenitor cells and contribute to bone adaptation.

Adaptation, Physiological↗

PubMed2000

Prism adaptation in normal aging: slower adaptation rate and larger aftereffect.

The effect of aging on prism adaptation, a motor learning paradigm, was evaluated. Different measures were obtained from a task consisting of throwing clay balls to a target in front of the subjects before, during, and after wearing prisms that deviate the visual field by several degrees. When performing the task without wearing the prisms, the aged subjects showed a larger hit variance, whereas the young subjects hit closer to the target. When donning the prisms, the aged group adapted more slowly than the controls, although after throwing all the balls both groups showed the same adaptation levels. After removing the prisms, the aged group showed a larger aftereffect. These findings suggest that the aftereffect requires the involvement of non-cognitive and cognitive processes and indicate that both adaptation and aftereffect are influenced by aging.

Adaptation, Physiological↗

PubMed2000

Adaptability in the workplace: development of a taxonomy of adaptive performance.

The purpose of this research was to develop a taxonomy of adaptive job performance and examine the implications of this taxonomy for understanding, predicting, and training adaptive behavior in work settings. Two studies were conducted to address this issue. In Study 1, over 1,000 critical incidents from 21 different jobs were content analyzed to identify an 8-dimension taxonomy of adaptive performance. Study 2 reports the development and administration of an instrument, the Job Adaptability Inventory, that was used to empirically examine the proposed taxonomy in 24 different jobs. Exploratory factor analyses using data from 1,619 respondents supported the proposed 8-dimension taxonomy from Study 1. Subsequent confirmatory factor analyses on the remainder of the sample (n = 1,715) indicated a good fit for the 8-factor model. Results and implications are discussed.

Adaptation, Psychological↗

PubMed2001

Adaptation of primate cell-adapted hepatitis A virus strain HM175 to growth in guinea pig cells is independent of mutations in the 5' nontranslated region.

Previous studies of hepatitis A virus (HAV) genotypes after adaptation of wild-type virus to growth in cell cultures of primate origin identified determinants for growth in cell culture in the viral 2B and 2C protein-coding regions of the genome and demonstrated that an increased growth efficiency in a particular cell line was achieved by subsequent mutations in the 5' nontranslated region (5'NTR). The results reported in this study demonstrate that the passage of HAV adapted to primate BS-C-1 cells in guinea pig cells resulted in increased growth efficiency in the rodent cells and decreased growth efficiency in BS-C-1 cells. This adaptation occurred without mutation in the 5'NTR, but the viral 2B and 2C proteins seem to play a role during adaptation to the new environment, as one mutation occurred in each protein. Although the data presented here do not clearly identify which region of the viral genome underwent mutations to improve the interaction of the viruses with guinea pig proteins, they do confirm that the 5'NTR is not the only region responsible for providing host cell-specific information.

5' Untranslated Regions↗

PubMed2001

Evolutionary adaptation to temperature. IX. Preadaptation to novel stressful environments of Escherichia coli adapted to high temperature.

Stressful environments may be considered as those that reduce fitness, sometimes due in part to the increased metabolic expenditure required to sustain life. Direct adaptation to a stressor is expected to increase fitness and reduce maintenance metabolism, with the latter leading to increased biomass production. In this study, we test the general hypothesis that such adaptation to one stressor can preadapt organisms to novel stressful environments. Six lines of Escherichia coli propagated for 2,000 generations at 41-42 degrees C (42 group), a stressful temperature, were compared to six control lines propagated for 2,000 generations at 37degrees C (37 group) and to the common ancestor of both groups. We assayed biovolume yield (a measure of growth efficiency) and competitive fitness in the 42 group's selective high temperature environment as well as five novel stressful environments-acid, alkali, ethanol, high osmolarity and peroxide. As previously reported, at high temperature the 42 group had both higher yield and fitness than the 37 group and ancestor. In the novel environments, the 42 group generally produced yields higher than the 37 group (and marginally higher than the ancestor), but we found no differences in competitive fitness among the 37 and 42 groups and the ancestor. We also found that the performance of lines within groups was not correlated across stressful environments for either yield or relative fitness. Because previous adaptation to one stressor did not improve our measure of Darwinian fitness in novel stressful environments, we conclude that the 42 group shows no useful pre-adaptation, or cross-tolerance, to these types of environments.

Adaptation, Physiological↗

PubMed2004

Adaptive divergence vs. environmental plasticity: tracing local genetic adaptation of metamorphosis traits in salamanders.

In order to assess the significance of local adaptation relative to environmental plasticity on the evolution of life history traits, we analysed the possible genetic basis of differences between pond- and stream-breeding fire salamanders (Salamandra salamandra) in Germany. These salamanders typically deposit their larvae in small streams, where they grow until they are sufficiently large to metamorphose. However, some populations in Western Germany use ponds as larval habitat. Because habitat quality of streams differs from that of ponds one expects life history differences in the pond animals, which may result either from a plastic response or through genetic differentiation (i.e. local adaptation). Using a phylogeographical analysis of mitochondrial D-loop sequences, we show that both stream and pond populations in Western Germany are derived from a single lineage that recolonized following the last glaciation. This finding suggests that pond breeding originated very recently. Our studies of habitat quality and metamorphic behaviour of larvae in natural ponds and streams disclosed that pond larvae experience a significantly reduced food supply and greater risk of drying than do stream larvae. Pond larvae metamorphose earlier at the cost of reduced mass. Common-environment experiments with pond and stream larvae show that metamorphic behaviour of pond larvae under limited-food conditions is determined genetically and is not simply a plastic response to the differing habitat conditions. These results show that phenotypic plasticity is less important than local adaptation in explaining differences in ecological diversification within this species and suggests the possibility of rapid evolution of genetic adaptations when new habitats are exploited.

Adaptation, Physiological↗

PubMed1995

Motor adaptation to Coriolis force perturbations of reaching movements: endpoint but not trajectory adaptation transfers to the nonexposed arm.

1. Reaching movements made in a rotating room generate Coriolis forces that are directly proportional to the cross product of the room's angular velocity and the arm's linear velocity. Such Coriolis forces are inertial forces not involving mechanical contact with the arm. 2. We measured the trajectories of arm movements made in darkness to a visual target that was extinguished at the onset of each reach. Prerotation subjects pointed with both the right and left arms in alternating sets of eight movements. During rotation at 10 rpm, the subjects reached only with the right arm. Postrotation, the subjects pointed with the left and right arms, starting with the left, in alternating sets of eight movements. 3. The initial perrotary reaching movements of the right arm were highly deviated both in movement path and endpoint relative to the prerotation reaches of the right arm. With additional movements, subjects rapidly regained straight movement paths and accurate endpoints despite the absence of visual or tactile feedback about reaching accuracy. The initial postrotation reaches of the left arm followed straight paths to the wrong endpoint. The initial postrotation reaches of the right arm had paths with mirror image curvature to the initial perrotation reaches of the right arm but went to the correct endpoint. 4. These observations are inconsistent with current equilibrium point models of movement control. Such theories predict accurate reaches under our experimental conditions. Our observations further show independent implementation of movement and posture, as evidenced by transfer of endpoint adaptation to the nonexposed arm without transfer of path adaptation. Endpoint control may occur at a relatively central stage that represents general constraints such as gravitoinertial force background or egocentric direction relative to both arms, and control of path may occur at a more peripheral stage that represents moments of inertia and muscle dynamics unique to each limb. 5. Endpoint and path adaptation occur despite the absence both of mechanical contact cues about the perturbing force and visual or tactile cues about movement accuracy. These findings point to the importance of muscle spindle signals, monitoring of motor commands, and possibly joint and tendon receptors in a detailed trajectory monitoring process. Muscle spindle primary and secondary afferent signals may differentially influence adaptation of movement shape and endpoint, respectively.

Adaptation, Physiological↗