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At least 217 records · Page 12Linked to original sources
PubMed1990

Training-induced skeletal muscle adaptations are independent of systemic adaptations.

To isolate the peripheral adaptations to training, five normal subjects exercised the nondominant (ND) wrist flexors for 41 +/- 11 days, maintaining an exercise intensity below the threshold required for cardiovascular adaptations. Before and after training, intracellular pH and the ratio of inorganic phosphate to phosphocreatine (Pi/PCr) were measured by 31P magnetic resonance spectroscopy. Also maximal O2 consumption (VO2 max), muscle mass, and forearm blood flow were determined by graded systemic exercise, magnetic resonance imaging, and venous occlusion plethysmography, respectively. Blood flow, Pi/PCr, and pH were measured in both forearms at rest and during submaximal wrist flexion at 5, 23, and 46 J/min. Training did not affect VO2 max, exercise blood flow, or muscle mass. Resting pH, Pi/PCr, and blood flow were also unchanged. After training, the ND forearm demonstrated significantly lower Pi/PCr at 23 and 46 J/min. Endurance, measured as the number of contractions to exhaustion, also was increased significantly (63%) after training in the ND forearm. We conclude that 1) forearm training results in a lower Pi/PCr at identical submaximal work loads; 2) this improvement is independent of changes in VO2 max, muscle mass, or limb blood flow; and 3) these differences are associated with improved endurance and may reflect improved oxidative capacity of skeletal muscle.

Adaptation, Physiological↗
PubMed2003

Closed-form expressions of some stochastic adapting equations for nonlinear adaptive activation function neurons.

In recent work, we introduced nonlinear adaptive activation function (FAN) artificial neuron models, which learn their activation functions in an unsupervised way by information-theoretic adapting rules. We also applied networks of these neurons to some blind signal processing problems, such as independent component analysis and blind deconvolution. The aim of this letter is to study some fundamental aspects of FAN units' learning by investigating the properties of the associated learning differential equation systems.

Action Potentials↗
PubMed2024

Adaptive or non-adaptive? Cranial evolution in a radiation of miniaturized day geckos.

Lygodactylus geckos represent a well-documented radiation of miniaturized lizards with diverse life-history traits that are widely distributed in Africa, Madagascar, and South America. The group has diversified into numerous species with high levels of morphological similarity. The evolutionary processes underlying such diversification remain enigmatic, because species live in different ecological biomes, ecoregions and microhabitats, while suggesting strikingly high levels of homoplasy. To underscore this evolutionary pattern, here we explore the shape variation of skull elements (i.e., cranium, jaw and inner ear) using 3D geometric morphometrics and phylogenetic comparative methods on computed tomography scans (CT-scan) of a sample encompassing almost all recognized taxa within Lygodactylus. The results of this work show that skull and inner ear shape variation is low (i.e., there is high overlapping on the morphospace) across geographic regions, macrohabitats and lifestyles, implying extensive homoplasy. Furthermore, we also found a strong influence of allometry shaping cranial variation both at intra and interspecific levels, suggesting a major constraint underlying skull architecture, probably as a consequence of its miniaturization. The remaining variation that is not allometric is independent of phylogeny and ecological adaptation and can probably be interpreted as the result of intrinsic developmental plasticity. This, in turn, supports the interpretation that speciation in this group is largely concordant with a non-adaptive hypothesis, which results mainly from vicariant processes.

Animals↗
PubMed1999

[In vitro comparison of marginal adaptation of various filling materials. I. Effect of the filling material on marginal adaptation].

In a two-month in vitro experiment cervical marginal adaptation was examined in relation to the preparation, filling method and restorative material. Fifty Class II cavities were prepared in fifty extracted sound human premolar and molar teeth extending to the approximal cement-enamel junction. The cavities to receive composite restorations were bevelled at the vestibulo-occlusal and -approximal enamel margins, the other aspects of the cavity enamel and gingival margins at the cement-enamel junction being prepared conventionally. The cavities for amalgam were prepared and filled conventionally. The specimens were cycled in different buffer solutions and temperature, modelling possible variations in the oral environment and examined with SEM. The results were analysed using ANOVA. The best marginal adaptation among the composites was achieved with Charisma, Estilux Posterior, Durafil and Prisma AP. H at the bevelled enamel margins, the worst marginal fit was with Heliomolar and Polofil. It was concluded, that adhesive technique reduces, but does not eliminate marginal leakage.

Analysis of Variance↗
PubMed1990

[The interrelations and essence of adaptation and disease (apropos the article by V. N. Galankin The interrelationship of adaptation and disease in phylo- and ontogeny)].

The views by I. V. Davydovskiĭ and V. N. Galankin are considered and their similarity is shown. The original opinion of the author is as follows: (1) the adaptation and disease are relatively independent properties of the organism and, thus, are interrelated as parts of the whole; (2) both adaptation and disease are included into the essence of the organism but are not identical to the essence of each other.

Adaptation, Physiological↗
PubMed1982

Rapid perceptual adaptation to high gravitoinertial force levels: evidence for context-specific adaptation.

Subjects exposed to periodic variations in gravitoinertial force (2-G peak) in parabolic flight maneuvers quickly come to perceive the peak force level as having decreased in intensity. By the end of a 40-parabola flight, the decrease in apparent force is approximately 40%. On successive flight days, the apparent intensity of the force loads seems to decrease as well, indicating a cumulative adaptive effect. None of the subjects reported feeling abnormally "flight" for more than a minute or two after return to 1-G background force levels. The pattern of findings suggests a context-specific adaptation to high-force levels.

Adaptation, Physiological↗
PubMed1994

Sibling adaptation to childhood cancer collaborative study: prevalence of sibling distress and definition of adaptation levels.

A multisite collaborative study assessed the frequency and intensity of emotional/behavioral distress in siblings of children with cancer. A sample of 254 siblings, aged 4 to 18 years, and their parents completed interviews and self-report measures 6 to 42 (average 22.5) months after diagnosis of cancer in a brother or sister. Matched controls were obtained from respondents to the Child Health Supplement of the National Health Interview Survey administered in 1988 (CHS88). Before diagnosis, the prevalence of parent-reported emotional/behavioral problems among siblings was similar to that in the general population (7.7% vs 6.3%; p = not significant). After diagnosis, prevalence rose to 18% among siblings. When siblings were grouped according to the presence or absence of problems exacerbated by and/or arising after diagnosis, four levels of adaptation, consistent with scores on the Behavior Problem Scales from the CHS88, emerged. This differentiation may help explain inconsistencies in sibling response reported previously and provides a framework for investigating factors that enhance adaptation.

Adaptation, Psychological↗
PubMed1993

Myocardial adaptation to stress from the viewpoint of adaptation and development.

Myocardial adaptation to stress and development includes reorganization of subcellular systems. Using a myothermal method, changes in the contractile protein system were investigated across species (rat, rabbit, human myocardium) and in consequence of hemodynamic (volume overload human, pressure overload rabbit myocardium) or hormonal stresses (hypothyroid rat, hyperthyroid rabbit myocardium). Mechanical and myothermal measurements were performed in isometrically contracting right or left ventricular muscle strips and the force-time integral of the individual crossbridge cycle was calculated from heat and force data. Within species, crossbridge force-time integral increased by 85% from control human to volume overload human myocardium. Crossbridge force-time integral increased by 100% from control to hypothyroid rat myocardium. In rabbit myocardium, crossbridge force-time integral increased by 164% in pressure overload and decreased by 47% in hyperthyroid compared to control myocardium. Across species, crossbridge force-time integral was smallest in control rat myocardium (0.16 +/- 0.01 pNs) and increased in the order: control rat < hyperthyroid rabbit < hypothyroid rat, control rabbit < control human < pressure overload rabbit < volume overload human myocardium (0.96 +/- 0.01 pNs). Within and across species, crossbridge force-time integral was positively correlated with time to peak tension (r = 0.86; p < 0.05) and negatively correlated with maximum rate of tension rise (r = -0.85; p < 0.05) and maximum rate of tension fall (r = -0.78; p < 0.05). Furthermore, there were significant correlations between crossbridge force-time integral and total activity related heat (r = -0.81; p < 0.05) as well as total activity related heat per tension-time integral (r = -0.89; p < 0.005). Thus, the close relationship between crossbridge force-time integral and myocardial function within and across species demonstrates that alterations of crossbridge force-time integral reflect an important mechanism of subcellular adaptation to stress from a mechanical point of view. Moreover, alterations of the crossbridge force-time integral have pronounced effects on energy consumption in the different types of myocardium.

Adaptation, Physiological↗
PubMed1977

[Influence of adaptation to altitude hypoxia and subsequent de-adaptation on the retention of a temporary connection].

Adaptation to simulated altitude hypoxia was followed by a significant increase of the degree of retention of active avoidance of the conditioned reflex. Twenty four hours after the reflex elaboration the adapted rats required only half of conditioned and unconditioned stimulus combinations in the reflex retention test than control ones. This effect was reproduced 1 and 5 days after the cessation of hypoxic training. The obtained increase in the degree of the conditioned reflex retention disappeared during deadaptation 10 and 27 days after the cessation of hypoxic training.

Adaptation, Physiological↗
PubMed1977

The role of the parathyroids for the adaptation to a low calcium intake. 5. The long-term effect of parathyroidectomy on the adaptation to a low calcium intake in adult rats with special reference to the metabolism of vitamin D.

One-year-old selectively parathyroidectomized rats showed a normalization of their plasma calcium level to above 4.1 mEq/l in 38% within 18 weeks on a normal dietary intake of calcium and inorganic phosphate but low in vitamin D. On a low level of dietary calcium, normalization did not occur in any of the parathyroidectomized animals. The conversion of 25-hydroxycholecalciferol into the active metabolite of vitamin D, 1,25-dihydroxycholecalciferol, by the kidneys was stimulated by a low dietary intake of calcium in intact animals and the accumulation of this metabolite was increased in small intestine mucosa. This adaptory increase in the level of intestinal 1,25-dihydroxycholecalciferol was not disturbed by selective parathyroidectomy, nor the synthesis by the kidneys. The synthesis reached a limit above which no further increase occurred despite the prevailing hypocalcemia possibly through an influence of the concomitant hyperphosphatemia. The renal synthesis and intestinal accumulation of 1,25-dihydroxycholecalciferol were directly related to the intestinal net absorption of dietary calcium, which we have reported on previously. Although increased, the endogenous level of 1,25-dihydroxycholecalciferol was too low to accomplish mobilization of skeletal calcium necessary for adaptation to a low calcium intake, as we have reported elsewhere. Thus, for adaptation skeletal calcium reserves must become mobilized through stimulated parathyroid activity with resulting osteoporosis. The parathyroids were found to have no direct regulatory influence upon the synthesis of 1,25-dihydroxycholecalciferol.

Adaptation, Physiological↗
PubMed1997

Sibling Adaptation to Childhood Cancer Collaborative Study: the association of sibling adaptation with maternal well-being, physical health, and resource use.

This multi-institutional study investigated the association of behavioral/emotional adaptation among siblings of children with cancer with maternal general well-being, physical health, and resource use. One hundred seventy siblings and mothers completed standardized interviews and self-report measures 6 to 42 months after the cancer was diagnosed. As a group, mothers of children with cancer reported significantly lower levels of well-being than matched controls. When stratified according to the level of the sibling's behavioral/emotional adaptation, mothers of siblings in the Dysfunctional group (1) reported the lowest levels of well-being; (2) during the preceding year, were more likely to have sought professional services than mothers of children in the Resilient group; and (3) were least likely to have found social support helpful. Our results support an association between maternal well-being and sibling adjustment but show it is unlikely that nonspecific social support will improve adjustment. The rationale for problem-solving training for mothers is provided.

Adaptation, Psychological↗
PubMed1995

Teenage childbearing. An adaptive strategy for the socioeconomically disadvantaged or a strategy for adapting to socioeconomic disadvantage?

OBJECTIVE: To examine the relation between childbearing and educational and vocational achievements of American females high school students. DATA SOURCE: Articles published in English during the past decade about the educational, vocational, and socioeconomic sequelae of childbearing among female high school students. DATA SELECTION: Articles that did not contain data about the relation between adolescent childbearing and educational and vocational achievement were excluded. DATA SYNTHESIS: Most females who begin childbearing during adolescence obtain less schooling and poorer-paying jobs than do females who postpone childbearing. The reasons for this are elusive. Differences in the family and cultural backgrounds of early (high school-age) and later (18 years and older) childbearers explain some but not all of the association between early childbearing and educational and vocational underachievement. The effect of childbearing preferences on the educational and vocational achievements of teenagers has not been studied adequately. Lack of concrete information could result in underestimation of the effect of early childbearing on the socioeconomic well-being of young Americans, and create the impression that adolescent pregnancy is an adaptive response to urban poverty. CONCLUSIONS: As much as the long-term socioeconomic sequelae of adolescent childbearing reflect factors that influence the judgments young people make about the costs and benefits of contraception and parenthood, adolescent childbearing is a means of adapting to urban poverty. Thus postponing adolescent conceptions and parenthood may have a less important effect on the socioeconomic well-being of young Americans than expected.

Adolescent↗
PubMed1982

Simulation of adaptive modification of the vestibulo-ocular reflex with an adaptive filter model of the cerebellum.

An adaptive linear filter model of the cerebellum (Fujita, 1982), which functions as a phase lead or lag compensator with learning capability, is applied to a problem of the cerebellar control of the vestibuloocular reflex (VOR). Under the assumption that the cerebellar flocculus accounts for adaptive modification of dynamic characteristics of the VOR, the cerebellar model was incorporated into a linear control model of the oculomotor system. The results of a simulation study are in good agreement with experimental data on eye movement.

Animals↗
PubMed1977

Cold adapted variants of influenza A. II. Comparison of the genetic and biological properties of ts mutants and recombinants of the cold adapted A/AA/6/60 strain.

The genetic and biological properties of 13 recombinant influenza A clones derived at 25 degrees C from the A/AA/6/60-cold variant (by crosses with 4 different wild type strains) were compared with a set of 5-FU induced ts-mutants. The 5-FU mutants had previously been placed into 7 complementation-recombination groups; the A/AA/6/60-cold parent (PI-7) and the 12 cold recombinant clones which were ts were shown to share a lesion with only one of these groups. The parental strain and 5 recombinant clones were evaluated for replication in the lungs and nasal turbinates of hamsters. Each virus appeared to be attenuated; genetic stability correlated with the level of viral replication in the hamster lung, i.e., viruses which grew best showed a tendency to revert to the ts+ phenotype. Characterization of the ts+ revertants for the presence of the cold adaptation property revealed that these viruses exhibited a spectrum of cold adaptation properties. Two viruses, PI-7 (the parental cold variant) and the CR6 recombinant (A/Queensland/6/72) did not revert in either the lungs or nasal turbinates of hamsters.

Animals↗
PubMed2003

Uptake and metabolism of pyrrolizidine alkaloids in Longitarsus flea beetles (Coleoptera: Chrysomelidae) adapted and non-adapted to alkaloid-containing host plants.

Several Longitarsus flea beetle species sequester pyrrolizidine alkaloids acquired from their Asteraceae and Boraginaceae host plants. We carried out feeding and injection experiments using radioactively labeled pyrrolizidine alkaloids to investigate the physiological mechanisms of uptake, metabolism and storage of alkaloids in adult beetles. We examined six Longitarsus species belonging to different phylogenetic clades in a comparative approach. All species that accepted pyrrolizidine alkaloids in a preceding food choice study showed the ability both to store pyrrolizidine alkaloid N-oxides and to metabolize tertiary pyrrolizidine alkaloids into their N-oxides. Regardless of whether the beetles' natural host plants contain pyrrolizidine alkaloids or not, these species were found to possess an oxidizing enzyme. This oxygenase appears to be specific to pyrrolizidine alkaloids: [3H]Atropine and [14C]nicotine, two alkaloids not related to pyrrolizidine alkaloids, were neither stored nor N-oxidized by any of the tested species. One species, L. australis, that strictly avoids pyrrolizidine alkaloids behaviorally, exhibited a lack of adaptations to pyrrolizidine alkaloids on a physiological level as well. After injection of tertiary [14C]senecionine, beetles of this species neither N-oxidized nor stored the compounds, in contrast to L. jacobaeae, an adapted species that underwent the same treatment. L. jacobaeae demonstrated the same efficiency in N-oxidation and storage when fed or injected with tertiary [14C]senecionine.

Animals↗
PubMed1982

Adaptation of retinal dopamine neuron activity in light-adapted rats to darkness.

The activity of the retinal dopamine neurons was studied in light-adapted rats exposed to darkness for periods ranging from 10 min to 15 h. Dihydroxyphenylalanine (DOPA) accumulation, following inhibition of L-aromatic amino acid decarboxylase with NSD-1015, was used as an index of dopamine neuronal activity. After only 10 min of darkness, DOPA accumulation had decreased to levels found in rats dark-adapted for 15 h.

Acclimatization↗
PubMed2006

Aging of the immune system: how much can the adaptive immune system adapt?

The competency of the adaptive immune function decreases with age, primarily because of the decline in production of naive lymphocytes in the bone marrow and thymus as well as the expansion of incompetent memory lymphocytes. Here I discuss the recent progress on age-associated changes in lymphocytes and their effect on the adaptive immune system.

Aged↗