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At least 325 records · Page 18Linked to original sources
PubMed2003

A methodological note on nonlinear time series analysis: is the open- and closed-loop model of Collins and De Luca (1993) a statistical artifact?

The authors reexamined, theoretically and empirically, the method proposed by J. J. Collins and C. D. De Luca (1993) for the analysis of center-of-pressure trajectories. The main argument in this article is that Collins and De Luca's approach is not adapted to the analysis of bounded time series and leads to statistical artifacts such as underestimation of the diffusion process for long-term intervals. The open- and closed-loop model developed by Collins and De Luca is a direct consequence of those statistical problems. Applying more classical methods, such as rescaled range analysis or detrended fluctuation analysis, the authors show that center-of-pressure trajectories can be modeled as continuous, antipersistent fractional Brownian motion. More specifically, those trajectories behave like 1/f noise, a ubiquitous feature in adaptive biological systems.

Humans↗
PubMed2006

Global use of alcohol, drugs and tobacco.

Humans have always used drugs, probably as part of their evolutionary and nutritional heritage. However, this previous biological adaptation is unlikely to be so in the modern world, in which 2 billion adults (48% of the adult population) are current users of alcohol, 1.1 billion adults (29% of the adult population) are current smokers of cigarettes and 185 million adults (4.5% of the adult population) are current users of illicit drugs. The use of drugs is determined largely by market forces, with increases in affordability and availability increasing use. People with socio-economic deprivation, however measured, are at increased risk of harmful drug use, as are those with a disadvantaged family environment, and those who live in a community with higher levels of substance use. Substance use is on the increase in low-income countries which, in the coming decades, will bear a disproportionate burden of substance-related disability and premature death.

Africa↗
PubMed2002

Chronic tolerance to nicotine in humans and its relationship to tobacco dependence.

Chronic tolerance to any drug of abuse traditionally has been thought critical to understanding drug dependence. This paper reviews research on chronic pharmacodynamic tolerance to nicotine in humans. An overview of tolerance and a discussion of methodological issues are first presented, followed by examination of cross-sectional comparisons of tolerance between groups differing in smoking history, as well as the few prospective studies of change in tolerance after quitting smoking. The relationship of nicotine tolerance to tobacco dependence is then evaluated. While somewhat modest in size, the literature on chronic tolerance to nicotine in humans is reasonably consistent in showing clear evidence of tolerance to subjective mood effects but little or no tolerance to cardiovascular, performance or other nicotine effects, within the limitations inherent in most human research on tolerance. However, this research also indicates that chronic tolerance to nicotine is not closely associated with tobacco dependence: non-dependent and dependent smokers are equally tolerant; tolerance declines very little even years after quitting; and tolerance before quitting may have no relationship to clinical outcome of a cessation attempt. Recent research from the alcohol and substance abuse fields is consistent with the notion that tolerance has little clinical utility in determining dependence. These results question the relevance of nicotine tolerance to dependence and suggest that research into mechanisms of tolerance, while important for understanding biological adaptation, may not elucidate factors responsible for nicotine dependence. Future research should focus on whether dependence may be related to tolerance or to other, as yet unexamined, effects of nicotine, including conditioned tolerance effects, and on the possibility that tolerance may influence the early onset of dependence in teens even if apparently unrelated to maintenance of dependence in adult smokers.

Cross-Sectional Studies↗
PubMed2003

Hidden messages in the nef gene of human immunodeficiency virus type 1 suggest a novel RNA secondary structure.

The coexistence of multiple codes in the genome of human immunodeficiency virus type 1 (HIV-1) was analyzed. We explored factors constraining the variability of the virus genome primarily in relation to conserved RNA secondary structures overlapping coding sequences, and used a simple combination of algorithms for RNA secondary structure prediction based on the nearest-neighbor thermodynamic rules and a statistical approach. In our previous study, we applied this combination to a non- redundant data set of env nucleotide sequences, confirmed the conservative secondary structure of the rev-responsive element (RRE) and found a new RNA structure in the first conserved (C1) region of the env gene. In this study, we analyzed the variability of putative RNA secondary structures inside the nef gene of HIV-1 by applying these algorithms to a non-redundant data set of 104 nef sequences retrieved from the Los Alamos HIV database, and predicted the existence of a novel functional RNA secondary structure in the beta3/beta4 regions of nef. The predicted RNA fold in the beta3/beta4 region of nef appears in two forms with different loop sizes. The loop of the first fold consists of seven nucleotides (positions 494-500), with consensus UCAAGCU appearing in 79% of sequences. The other has a five-base loop (positions 495-499) with consensus CAAGC. The difference in size between these two loops may reflect the difference between respective counterparts in the hairpin recognition. This may also have an adaptive biological significance.

Algorithms↗
PubMed1996

Natural history of nutrition in chronic renal failure.

Dietetic manipulation significantly influences the progression of renal failure in laboratory animals. Clinical results in humans are contradictory. The aim of the study was epidemiological research on a large sample of kidney disease patients to verify whether renal failure influences nutrient intake before dietetic manipulation. Four hundred and forty-one consecutive, non-selected adult patients with renal insufficiency (creatinine 133-963 mumol, mean 301 +/- 178 mumol in male, 288 +/- 156 mumol/l in female) and 43 kidney disease patients without renal failure were enrolled in the prospective study in the period 1988-1995. Interview at the time of the first nephrological check was performed by only one dietician; the record by recall of intake over 7 days with quantitative assessment was collected with the assistance of nutritional dossier and photographic measures. The patients with renal failure consume energy, proteins, lipids and carbohydrates in lesser quantities than the national population of the same geographical area, but the total lipid and monounsaturated fatty acid intake is higher compared with Italian dietary reference values. In patients with renal failure mean protein intake was 1.02 +/- 0.2 g/kg/day in males and 0.96 +/- 0.2 g/kg/day in females; mean lipid intake was 1.10 +/- 0.2 g/kg/day in males and 1.17 +/- 0.3 g/kg/day in females; mean carbohydrate intake was 3.7 +/- 1.1 g/kg/day in males and 3.49 +/- 1 g/kg/day in females. The nutrition alterations observed in chronic renal failure may be a biological adaptation due to neurological changes affecting the sense of taste.

Adult↗
PubMed2002

What, if anything, is a Tilapia?-mitochondrial ND2 phylogeny of tilapiines and the evolution of parental care systems in the African cichlid fishes.

We estimated a novel phylogeny of tilapiine cichlid fish (an assemblage endemic to Africa and the Near East) within the African cichlid fishes on the basis of complete mitochondrial NADH dehydrogenase subunit 2 (ND2) gene sequences. The ND2 (1,047 bp) gene was sequenced in 39 tilapiine cichlids (38 species and 1 subspecies) and in an additional 14 nontilapiine cichlid species in order to evaluate the traditional morphologically based hypothesis of the respective monophyly of the tilapiine and haplochromine cichlid fish assemblages. The analyses included many additional cichlid lineages, not only the so-called tilapiines, but also lineages from Lake Tanganyika, east Africa, the Neotropics and an out-group from Madagascar with a wide range of parental care and mating systems. Our results suggest, in contrast to the historical morphology-based hypotheses from Regan (1920, 1922 ), Trewavas (1983), and Stiassny (1991), that the tilapiines do not form a monophyletic group because there is strong evidence that the genus Tilapia is not monophyletic but divided into at least five distinct groups. In contrast to this finding, an allozyme analysis of Pouyaud and Agnèse (1995), largely based on the same samples as used here, found a clustering of the Tilapia species into only two groups. This discrepancy is likely caused by the difference in resolution power of the two marker systems used. Our data suggest that only type species Tilapia sparrmanii Smith (1840) should retain the genus name TILAPIA: One particular group of tilapiines (composed of genera Sarotherodon, Oreochromis, Iranocichla, and Tristramella) is more closely related to an evolutionarily highly successful lineage, the haplochromine cichlids that compose the adaptive radiations of cichlid species flocks of east Africa. It appears that the highly adaptable biology of tilapiines is the ancestral state for all African cichlids and that the more stenotypic lifestyle of the haplochromine cichlids is derived from this condition. We reconstructed the evolution of the highly variable parental care systems on the basis of the most inclusive composite phylogeny to date of the African, Neotropical, and Madagascan cichlids with special emphasis on a group of tilapiines comprising the substrate-spawning genus Tilapia, and the mouthbrooding genera Sarotherodon and OREOCHROMIS: We demonstrate several independent origins of derived mouthbrooding behaviors in the family Cichlidae.

Biological Evolution↗
PubMed1991

A process-oriented model of human motor behavior: toward a theory-based rehabilitation approach.

The purpose of this article is to present a behavioral model of human motor acts that may have relevance for therapeutic procedures aimed at the restoration of motor function after neurological or orthopedic problems. A key point of this model is that motor behavior is the result of an integrated and adaptive biological system. Cognitive, perceptual, and motor mechanisms are not independent elements, but are viewed as inseparable parts of this functional system. Implications for therapy are discussed. [Mulder T. A process-oriented model of human motor behavior: toward a theory-based rehabilitation approach.

Biomechanical Phenomena↗
PubMed1997

Human milk protein does not limit growth of breast-fed infants.

BACKGROUND: The efficiency with which breast- and formula-fed infants utilize dietary nutrients is likely to provide insight into their relative requirements for the growth process. METHODS: We measured longitudinal changes in growth, body composition, and dietary intakes in breast- and formula-fed infants and estimated the gross efficiency with which dietary nitrogen and energy were used for lean body mass and body fat deposition. Lean body mass and body fat were determined in 10 breast-fed and 10 formula-fed infants at 6-week intervals during the first 24 weeks of life by the 18O dilution technique. Dietary nitrogen and energy intakes were determined from the amount of milk and food consumed and the nutrient content of the feedings. The gross efficiency of nutrient utilization was calculated for each infant from the cumulative dietary intake and the change in body composition with time. RESULTS: Length and weight gains and lean body mass and body fat accretion during the first 24 weeks of life were similar between breast- and formula-fed infants despite significantly higher nitrogen and energy intakes of the formula-fed group. The gross efficiency of dietary nitrogen utilization for lean body mass deposition was almost two-fold lower in formula- than in breast-fed infants, whereas the efficiency of dietary energy utilization for lean body mass and body fat deposition was similar between groups. Despite apparent differences in the efficiency of nitrogen utilization, there was no association between lean body mass deposition and dietary protein intake, implying that human milk protein does not limit growth quantitatively in breast-fed infants. CONCLUSIONS: These differences in nutrient utilization illustrate the biologic adaptability of human infants who are equipped with mechanisms that promote normal growth despite the variability of their nutrient intake.

Body Composition↗
PubMed2003

Do electrically stimulated sensory inputs and movements lead to long-term plasticity and rehabilitation gains?

Peripheral and cortical magnetic and electrical stimulation may find a therapeutic niche as augmentative rehabilitation interventions for lessening impairments and disabilities after brain and spinal cord injury. The momentum for these approaches arose from recent physiological studies that examined the effects of paradigms of stimulation on synaptic and biological adaptations within the cortex and lumbar cord. A case report about improvements made by Christopher Reeve is driving requests by patients with profound spinal cord injury for interventions that include resistance pedaling facilitated by electrical neuromuscular stimulation. Although the evidence for this particular approach is less than convincing, reorganization-inducing cortical and peripheral afferent stimulation protocols offer insights into the steps needed for scientific designs of these potential rehabilitation interventions.

Afferent Pathways↗
PubMed1979

Comparison and adaptation.

It has sometimes been suggested that the term adaptation should be reserved for differences with a known genetic basis. We argue that adaptation should be defined by its effects rather than by its causes as any difference between two phenotypic traits (or trait complexes) which increases the inclusive fitness of its carrier. This definition implies that some adaptations may arise by means other than natural selection. It is particularly important to bear this in mind when behavioural traits are considered. Critics of the 'adaptationist programme' have suggested that an important objection to many adaptive explanations is that they rely on ad-hoc arguments concerning the function of previously observed differences. We suggest that this is a less important problem (because evolutionary explanations generally claim some sort of generality and are therefore testable) than the difficulties arising from confounding variables. These are more widespread and more subtle than is generally appreciated. Not all differences between organisms are directly adapted to ecological variation. The form of particular traits usually constrains the form of value that other traits can take, presenting several obstacles to attempts to relate variation in morphological or behavioural characteristics directly to environmental differences. We describe some of the repercussions of differences in body size among vertebrates and ways in which these can be allowed for. In addition, a variety of evolutionary processes can produce non-adaptive differences between organisms. One way of distinguishing between these and adaptations is to investigate adaptive trends in phylogenetically different groups of species.

Adaptation, Biological↗
PubMedDate not supplied

Conservation-withdrawal reaction in infancy? An underdescribed entity.

Conservation-withdrawal is considered a biological non-pathological process subserving survival in circumstances which pose an extreme threat to an infant, child or adult. Although initially described in an infant, is reported frequency in that age group seems sparse. Four infants are described, three of whom presented with weight loss. Despite their mothers' assertions that their breast feeding was adequate, the three infants gained weight rapidly on complementary feeding and became more responsive. Previously they had passively accepted sub-optimal intakes, crying little and sleeping excessively. When their initial crying and objection went unheeded, they seemed to pass into a conservation-withdrawal state, conserving their energies, biologically adapting to their mothers' inability to provide adequate nutrition. These infants did not appear ill and investigations proved normal. With adequate feeding, rapid improvement was observed in their weight gain, activity and responsiveness with normal development. Their mothers' selective denial of their own inadequate breast supply resulted in their inability to perceive their infants appropriately, depriving them of their nutritional needs. Additional factors of emotional deprivation and neglect may have occurred in the fourth infant. The responses of these infants observed during their period of severe stress, may appropriately be characterised by Engel's conservation-withdrawal state.

Breast Feeding↗
PubMed1992

The chromosomal integration site for the Streptomyces plasmid SLP1 is a functional tRNA(Tyr) gene essential for cell viability.

The genetic element SLP1 exists in nature as a single DNA segment integrated into the genome of Streptomyces coelicolor. Upon mating with Streptomyces lividans, a closely related species, SLP1 undergoes precise excision from its chromosomal site and is transferred into the recipient where it integrates chromosomally. Previous work has shown that integration and excision involve site-specific recombination between a chromosomal site, attB, and a virtually identical sequence, attP, on SLP1. We demonstrate here by means of gene replacement that a tRNA(Tyr) sequence that overlaps part of the attB site of S. lividans is both biologically functional and essential for cell viability. The requirement for this tRNA gene has been used to stabilize the inheritance of a segrationally unstable plasmid in cells lacking a chromosomal attB site. The evolution of an essential DNA locus as an attachment site for a chromosomally integrating genetic element represents a novel mechanism of biological adaptation.

Base Sequence↗