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PubMed1979

Recalibration of the convergence system.

Adaptation to convergence-altering prism spectacles was studied. The subjects were trained for 8 min with either convergence-increasing or convergence-decreasing prisms. Before and after training they estimated the distance to a binocular dot varying in the stimulus it provided to convergence. Both the preadaptation and postadaptation estimates showed that the reciprocal of estimated target distance is linearly related to convergence. Further there was a consistent change in the direction of adaptation expected from the preadaptation to the postadaptation test. This change was accounted for in terms of a recalibration of the effective absolute convergence level.

Adaptation, Ocular↗
PubMed2005

Genomic adaptation to acidic environment: evidence from Helicobacter pylori.

The origin of new functions is fundamental in understanding evolution, and three processes known as adaptation, preadaptation, and exaptation have been proposed as possible evolutionary pathways leading to the origin of new functions. Here we examine the origin of an acid resistance mechanism in the mammalian gastric pathogen Helicobacter pylori, with reference to these three evolutionary pathways. The mechanism involved is that H. pylori, when exposed to the acidic environment in mammalian stomach, restricts the acute proton entry across its membrane by its increased usage of positively charged amino acids in the inner and outer membrane proteins. The results of our comparative genomic analysis between H. pylori, the two closely related species Helicobacter hepaticus and Campylobacter jejuni, and other relevant proteobacterial species are incompatible with the hypotheses invoking preadaptation or exaptation. The acid resistance mechanism most likely arose by selection favoring an increased usage of positively charged lysine in membrane proteins.

Adaptation, Biological↗
PubMed1989

Retinal adaptation effects on the patterned VEP and ERG.

The patterned visually evoked potential (pVEP) and patterned electroretinogram (pERG) after light and dark adaptation were investigated in 10 visually normal human observers. The influence of retinal preadaptation on the pVEP appeared to be dependent on the stimulus field size. With a 6 degree field size retinal adaptation effects were not apparent, but with a 12 degree field size the amplitudes of the dark-adapted steady-state pVEP (ssVEP) and transient pVEP (tVEP) were significantly larger than the light-adapted amplitudes. Similarly pERG's elicited by a 12 degree field size produced larger amplitude dark-adapted results. The implications of these findings are discussed. Monitoring the temporal changes in the pVEP subsequent to different retinal preadaptation levels proved to be inconclusive for the conditions studied.

Adaptation, Ocular↗
PubMed1991

Model of tonic accommodation after sustained near focus.

The effect of short-term near focus on tonic accommodation (TA) was previously investigated in 48 visually normal subjects. After sustained focus upon a near target for 10 min, all illumination was extinguished and the decay of accommodation was monitored for 20 min. We calculated from these results that accommodation decayed rapidly with a time constant of about 0.4 min, followed by a slower decay with a time constant of about 32 min. However, the asymptotic level remained slightly above the preadaptation level after 20 min in the dark. A feedback model with two parallel dynamic components (transient and decay), which summed with a "bias" element in the forward loop, was developed to account for the results. The gains of the dynamic elements were varied until the simulation curves matched the experimental adaptation and decay data. During the closed-loop adaptation phase, the outputs of the dynamic elements moved in opposite directions but combined to yield the overall accommodation step response. Moreover, when the model was subsequently open-looped in the dark, the transient component declined rapidly, whereas the decay component remained above the preadaptation level. When the 48 subjects were grouped equally into 4 refractive categories, somewhat different decay time courses could be simulated with changes in model parameter values.

Accommodation, Ocular↗
PubMed2004

Spatial compression and adaptation with the low vision telescope.

PURPOSE: Geometrical analysis of monocular visual information specifying distance shows that a low vision telescope compresses optically specified distances by a factor about equal to its magnification. Using a group of eight visually healthy adults, we investigated the initial perceptual effect of putting on a 2x Galilean telescope and the adaptation produced by wearing the telescope. METHODS: Viewing was monocular, and the environment was only visible through the telescope. Because the telescope reduced the field of view to 13 degrees , we also tested a different group of eight visually normal adults who wore a simple monocular tube that restricted the field of view to 13 degrees . We measured perceived distance in a corridor using a visually directed open-loop walking task with distances ranging from 4 to 8 m. For both groups, monocular distance perception was measured before putting on the viewing device (baseline), immediately after putting on the viewing device (preadaptation), after wearing the viewing device during a 30-minute period of visual-motor activities (postadaptation), and immediately after taking off the viewing device (aftereffect). RESULTS: Comparing preadaptation with baseline measurements, the viewing devices produced a 15.4% initial compression of perceived distance on average. Comparing aftereffect with baseline measurements, the adaptation period produced a negative aftereffect that was 56.5% of the initial compression, thus showing substantial adaptation. The initial compression and the adaptation were highly significant effects, but neither effect was significantly different for the telescope group and the tube group. CONCLUSION: We conclude that free head movements in a structured environment can largely overcome the optically specified compression of distance produced by the 2x magnification of a low vision telescope, but there remains a significant initial compression of perceived distance that is produced by the restricted field of view. This compression can be substantially reduced by a short period of interaction with the environment.

Adaptation, Physiological↗
PubMed2003

Apomixis in flowering plants: an overview.

Apomixis is a common feature of perennial plants, which occurs in ca. 60% of the British flora, but has been largely ignored by reproductive theoreticians. Successful individuals may cover huge areas, and live to great ages, favoured by 'symmetrical' selection. Apomixis is favoured by colonizing modes, for instance post-glacially. Despite its theoretical advantages, apomixis usually coexists with sexuality, suggesting 'hidden' disadvantages. Agamospermy (apomixis by seed) is relatively uncommon, but gains from the attributes of the seed. It pays agamospermy genes, which discourage recombination, to form co-adapted linkage groups, so that they become targets for disadvantageous recessive mutant accumulation. Consequently, agamospermy genes cannot succeed in diploids and agamosperms are hybrid and highly heterotic. Agamospermous endosperm may suffer from genomic imbalance, so that nutritious ovules, which can support embryos without endosperm, may be preadapted for agamospermy. When primary endosperm nucleus fertilization ('pseudogamy') continues as a requirement for many aposporous agamosperms, selfing sex becomes preadaptive and archesporial sex remains an option. Apomictic populations can be quite variable although apomictic families are much less variable than sexuals. Only in some diplosporous species does sex disappear completely, and in those species some release of variability may persist through somatic recombination. The search for an agamospermy gene suitable for genetic modification should target fertile sexuals with a single localized agamospermy (A) gene, which therefore lack a genetic load. The A gene should coexist alongside sexuality, so that it would be easy to select seedlings of sexual and asexual origins. Plants with sporophytic agamospermy provide all these attributes.

Magnoliopsida↗
PubMed2006

Differential expression and localization of early light-induced proteins in Arabidopsis.

The early light-induced proteins (Elips) in higher plants are nuclear-encoded, light stress-induced proteins located in thylakoid membranes and related to light-harvesting chlorophyll (LHC) a/b-binding proteins. A photoprotective function was proposed for Elips. Here we showed that after 2 h exposure of Arabidopsis (Arabidopsis thaliana) leaves to light stress Elip1 and Elip2 coisolate equally with monomeric (mLhcb) and trimeric (tLhcb) populations of the major LHC from photosystem II (PSII) as based on the Elip:Lhcb protein ratio. A longer exposure to light stress resulted in increased amounts of Elips in tLhcb as compared to mLhcb, due to a reduction of tLhcb amounts. We demonstrated further that the expression of Elip1 and Elip2 transcripts was differentially regulated in green leaves exposed to light stress. The accumulation of Elip1 transcripts and proteins increased almost linearly with increasing light intensities and correlated with the degree of photoinactivation and photodamage of PSII reaction centers. A stepwise accumulation of Elip2 was induced when 40% of PSII reaction centers became photodamaged. The differential expression of Elip1 and Elip2 occurred also in light stress-preadapted or senescent leaves exposed to light stress but there was a lack of correlation between transcript and protein accumulation. Also in this system the accumulation of Elip1 but not Elip2 correlated with the degree of PSII photodamage. Based on pigment analysis, measurements of PSII activity, and assays of the oxidation status of proteins we propose that the discrepancy between amounts of Elip transcripts and proteins in light stress-preadapted or senescent leaves is related to a presence of photoprotective anthocyanins or to lower chlorophyll availability, respectively.

Arabidopsis↗
PubMed1982

Phenotypical Temperature Adaptation of Protein Synthesis in Wheat Seedlings : QUALITATIVE ASPECTS. INVOLVEMENT OF AMINOACID:tRNA-LIGASES.

Phenotypical temperature adaptation of protein synthesis in wheat (Triticum aestivum L.) seedlings is not affected by darkness (etiolation), by partial inhibition of protein biosynthesis (10(-3)m fluorophenylalanine), or by changing the amino acid precursor and the radioisotope ([(3)H]valine instead of [(14)C]leucine). The temperature coefficient (mu), as well as the optimum temperature of in vivo protein synthesis, increases with rising preadaptation temperature, as normally observed. Protein turnover studies revealed that only proteins with a short half-life time (t((1/2)) = 2 to 4 hours) are labeled to a measurable extent during the temperature adaptation experiments. A heat-labile protein has been detected and partially characterized by means of polyacrylamide gradient gels. Leucine:tRNA-ligase (EC 6.1 1.4) from heat-pretreated wheat seedlings exhibits enhanced thermal stability. In Arrhenius curves, the upper transition point shifts from 30 to 34 degrees C, depending on preadaptation temperature. Only the leucine:tRNA-ligase extracted from heat-adapted plants is stable when the enzyme extracts are subjected to a 34 degrees C heat treatment.

Journal Article↗
PubMed1983

The development of early non-verbal communication: an evaluation of its meaning.

Communication and social preadaptation have interpretative problems in early interaction. Both have strong teleological commitment and are not therefore wholly appropriate. The mother-infant system gradually achieves the hallmark of true teleology largely because the mother acts as if the newborn's foetal-like behaviour had communicative significance. Viewing newborn behaviour as such is compatible with the biological principle of preadaptation which avoids vague assumptions about early behaviour being socially 'prewired'. It is recommended that the mother be given an observer's role as it may lead to a useful methodology for understanding early communication. Studying deviancy in early relationships is also considered.

Child Behavior↗
PubMedDate not supplied

Developmentally-regulated virulence factors of Trypanosoma cruzi and their relationship to evasion of host defences.

Developmental preadaptation of virulent stages of Trypanosoma cruzi correlates with their ability to survive and establish infection in mammalian hosts. Infective trypomastigote stages must first preadapt to survival in the extracellular milieu and then to the rigors of establishing an intracellular infection. Selected phenotypic variations in evading host defences have been correlated with expression of stage-specific proteins or functions. Resistance of trypomastigotes to complement-mediated killing correlates with the presence of a stage-specific molecule that exhibits an analogous function to mammalian decay-accelerating factor, and with the presence of a neuraminidase/trans-sialidase that transfers sialic acid moieties to the parasite surface, thereby enabling it to avoid complement activation. Trypomastigotes enter cells by a mechanism that involves sorting of cell surface receptors and avoids eliciting a respiratory burst. Once within a membrane-bound vacuole, which undergoes acidification, the neuraminidase/trans-sialidase and an acid-active, transmembrane pore-forming protein are released by the parasite and are capable of acting together to accelerate rupture of the vacuolar membrane and the parasite's escape into the cytoplasm of the host cell. Escape from the parasitophorous vacuole allows virulent stages of T. cruzi to avoid compartmental, non-oxidative killing mechanisms such as degradation by lysosomal hydrolases.

Animals↗
PubMed1979

The effect of L-alpha-amino-n-butyric acid on growth and production of extracellular isoleucine and valine by Eubacterium ruminantium and a related rumen isolate.

Two anaerobic rumen bacteria, Eubacterium ruminantium and a closely related isolate, were studied to determine the effect of the valine antimetabolite alpha-aminobutyric acid on growth and production of extracellular isoleucine and valine in an amino acid free medium. In the absence of alpha-aminobutyrate, these organisms actively excreted valine during growth (90-195 microgram/mL) but only accumulated limited concentrations of isoleucine (3-7 microgram/mL) in the culture broth. Growth of both organisms was reduced in the presence of 0.5-1.5% alpha-aminobutyrate but this inhibition was largely overcome by the use of preadapted inoculum. Metabolism of alpha-aminobutyrate was also increased using preadapted inoculum. During growth in the presence of 0.5-1.5% alpha-aminobutyrate, both organisms accumulated high concentrations of isoleucine (100-225 microgram/mL) while the normal accumulation of valine was unaffected. alpha-Ketobutyrate, a product of alpha-aminobutyrate metabolism, also stimulated isoleucine excretion by these organisms. The results are discussed in relation to the regulation of the biosynthetic pathways of isoleucine and valine in these rumen anaerobes and the potential significance of this amino acid excretion in ruminant nutrition.

Adaptation, Physiological↗
PubMed2002

How reading works: considerations from prehistory to the present.

Reading is not a "natural" human ability. Because reading was invented only 6,000 years ago there cannot have developed any central nervous system structures specifically for the purpose of mediating reading. The anthropological concept of preadaptation, which states that the evolution of a structure for one purpose can enable that structure to perform another, must be true for reading. The research discussed in this article looks into the functions that preadapted the brain for reading. Findings suggest that the ancient skills of gestural comprehension and animal tracking were the underpinnings of brain organization that permitted reading to occur.

Basal Ganglia↗
PubMed1985

Competition between Chlorellae in chimeric infections of Hydra viridis: the evolution of a stable symbiosis.

Aposymbiotic polyps of Hydra viridis were infected with one or two of the following strains of Chlorella: the native strain obtained from green H, viridis, and the originally non-symbiotic strains Fs and 211/8p cultured in vitro. Larvae of Artemia served as infecting vectors. Chimeric infections were obtained with two different Chlorella strains cohabiting in the same cells and polyps. In time, the chimeric infections disappeared and mixed populations of Hydra were formed with different strains of Chlorella in different polyps. We suggest that the Chlorella/Hydra symbiosis was initiated originally by an infection of preadapted hydra by preadapted chlorellae. Through intracellular interalgal competition and competition between dissimilar infected cells and polyps, the present-day stable symbiosis has evolved.

Animals↗
PubMed1988

Hypoxia-induced oxygen tolerance: maintenance of endothelial metabolic function.

Hypoxia (10%-12% O2) preadaptation for 4-7 days effectively protects rats from oxygen toxicity. The present study was designed to investigate the hypothesis that the lung's microvascular endothelium shares in development of oxygen tolerance and therefore that endothelial metabolic function would be protected from oxygen toxicity by prior adaptation to hypoxia. Since pulmonary oxygen toxicity decreases lung capillary angiotensin converting enzyme (ACE) activity, we assayed converting enzyme active sites in an isolated perfused rat lung preparation as a marker for the development of oxygen toxicity and tolerance. Rats were exposed to air, hypoxia (10% O2 for 4 days), hyperoxia (greater than 95% O2 for 2 days) alone, or hypoxia followed immediately by hyperoxia. Lung vascular ACE content was quantitated by measuring the single pass binding of an iodinated-converting enzyme inhibitor, 125I-MK351A, a derivative of lisinopril. Hypoxia adaptation per se had no effect on ACE content reflected in normal 125I-MK351A binding, whereas hyperoxia exposure caused a significant decrease in lung vascular ACE. Hyperoxia-induced decreases in ACE content were prevented partially by hypoxia adaptation, indicating that ACE content on luminal endothelial surfaces was protected from oxygen toxicity. In isolated perfused lungs 125I-MK351A binding reflects development of oxygen tolerance after hypoxia preadaptation and suggests that lung endothelial metabolic function is protected from oxygen toxicity.

Adaptation, Physiological↗
PubMed1987

Adaptation of the resting states of accommodation.

Without an adequate stimulus to focus, the eyes accommodate for a "resting state" that averages about 1.6 diopter (D) (62 cm). The resting state can be made more "myopic" by adaptation to a near accommodative or vergence stimulus. In the present experiment, 21 subjects were tested for adaptation to both types of stimuli. Resting state was measured before and after adaptation in the dark (dark focus) and in the presence of an illuminated empty field. The authors found that preadaptation resting states were more myopic in the light field than in the dark test conditions; accommodative and vergence stimuli produce myopic shifts in dark and light field resting states; and a subset of the subjects show much larger aftereffects in the light field conditions. These subjects also show the largest difference between preadaptation dark- and light-field measures. Differences between dark- and light-field measures of resting state in these and other experiments may require a re-examination of the hypothesis that there is a single resting state for each subject.

Accommodation, Ocular↗
PubMedDate not supplied

[Toxicity of etmozin under extreme conditions].

A study was made of the toxicity of etmozine injected into rats of both sexes intraperitoneally under usual conditions, into overheated rats, into rats adapted to pressure chamber hypoxia, and into rats preadapted to pressure chamber hypoxia. It was established that etmozine toxity in the overheated rats significantly lessened as compared to that in intact animals, whereas in the rats adapted to pressure chamber hypoxia and in the overheated rats preadapted to pressure chamber hypoxia, it significantly rose.

Adaptation, Physiological↗
PubMedDate not supplied

[Temperature dependence of the arginase activity of the plerocercoids of Triaenophorus nodulosus and Diphyllobothrium latum].

The effect of temperature on the arginase enzyme activity in Triaenophorus nodulosus and Diphyllobothrium latum was studied. The temperature optimum of arginase of T. nodulosus (definitive hosts are fishes) is at 27 degrees while in D. latum it is at 57 degrees. It has been inferred that a certain preadaptation of some enzyme properties (temperature optimum, thermostabolity) to a temperature regime of a definitive host takes place. Biochemical mechanisms of preadaptation of enzyme systems of helminths to temperature are discussed.

Adaptation, Physiological↗
PubMed1994

In vivo manipulation of the xanthophyll cycle and the role of zeaxanthin in the protection against photodamage in the green alga Chlorella pyrenoidosa.

Chlorella pyrenoidosa was grown in steady-state continuous cultures in either high or low light. Samples of these cultures were incubated in darkness (violaxanthin state) or in saturating light (zeaxanthin state). These samples were kept in the respective preadapted states throughout the entire photodamage treatment. Photodamage involved exposure to single-turnover flashes fired at a low (non-actinic) frequency. The damage caused by the light stress thus applied was monitored by changes in photosynthetic properties and pigment composition. Cells preadapted in the light resisted photodamage better than those kept in darkness. The low light grown cells were more vulnerable to photodamage than the high light grown cells. Our experimental approach permitted the equilibria between the components that participate in the xanthophyll cycle to be set without addition of inhibitors. Regardless of the total amount of violaxanthin being present, its conversion to anthera- and zeaxanthin is a prerequisite for protection. The protection is most effective for photosystem II. It appeared that antheraxanthin accumulates as a result of photodamaging flashes provided that these are fired in the presence of background light, i.e. with zeaxanthin present. From this, it is newly derived that the xanthophyll cycle operates in full in the light, including epoxidation of zeaxanthin. The latter conversion was also demonstrated in vitro, via nonenzymatic oxygen-dependent turnover of zeaxanthin into violaxanthin.

Carotenoids↗