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At least 919 records · Page 51Linked to original sources
PubMed1981

Trade-off between r-selection and K-selection in Drosophila populations.

Density-dependent genetic evolution was tested in experimental populations of Drosophila melanogaster subject for eight generations to natural selection under high (K-selection) or low (r-selection) population density regimes. The test consisted of determining at high and at low densities the per capita rate of population growth of the selected populations. At high densities, the K-selected populations showed a higher per capita rate of population growth than did r-selected populations, but the reverse was true at low densities. These results corroborate the predictions derived from formal models of density-dependent selection. However, no evidence of a trade-off in per capita rate of growth was observed in 25 populations of D. melanogaster, each homozygous for a different second chromosome sampled from a natural population.

Journal Article↗
PubMed1997

Protein engineering reveals ancient adaptive replacements in isocitrate dehydrogenase.

Evolutionary analysis indicates that eubacterial NADP-dependent isocitrate dehydrogenases (EC 1.1.1.42) first evolved from an NAD-dependent precursor about 3.5 billion years ago. Selection in favor of utilizing NADP was probably a result of niche expansion during growth on acetate, where isocitrate dehydrogenase provides 90% of the NADPH necessary for biosynthesis. Amino acids responsible for differing coenzyme specificities were identified from x-ray crystallographic structures of Escherichia coli isocitrate dehydrogenase and the distantly related Thermus thermophilus NAD-dependent isopropylmalate dehydrogenase. Site-directed mutagenesis at sites lining the coenzyme binding pockets has been used to invert the coenzyme specificities of both enzymes. Reconstructed ancestral sequences indicate that these replacements are ancestral. Hence the adaptive history of molecular evolution is amenable to experimental investigation.

Amino Acid Sequence↗
PubMed1997

The KH domain protein encoded by quaking functions as a dimer and is essential for notochord development in Xenopus embryos.

Mutations in the mouse indicate that quaking gene function is essential for both embryogenesis and for development of the nervous system. Recent isolation of the mouse quaking gene identified a putative RNA-binding protein containing a single KH domain. We have previously isolated the Xenopus homolog of quaking, Xqua, and shown that the sequence is highly conserved through evolution. Here, we report experimental data on the biochemical function of the quaking protein and its role during development. We demonstrate that the quaking protein expressed during early embryogenesis, pXqua357, can bind RNA in vitro, and we have mapped the regions of the protein that are essential for RNA binding. We present evidence that pXqua can form homodimers and that dimerization may be required for RNA binding. Oocyte injection experiments show that pXqua357 is located in both the nucleus and cytoplasm. In the Xenopus embryo, Xqua is first expressed during gastrulation in the organizer region and its derivative, the notochord. In later stage embryos, Xqua is expressed in a number of mesodermal and neural tissues. We demonstrate that disruption of normal Xqua function, by overexpression of a dominant inhibitory form of the protein, blocks notochord differentiation. Xqua function appears to be required for the accumulation of important mRNAs such as Xnot, Xbra, and gsc. These results indicate an essential role for the quaking RNA-binding protein during early vertebrate embryogenesis.

Animals↗
PubMed2002

Theoretical description of repeated surface-tension auto-oscillations.

A mathematical model is proposed to follow the behavior of a system where a droplet of a surfactant with limited solubility on the tip of a capillary under the free liquid surface dissolves in a container with a unity aspect ratio. Numerical simulations show that instability repeatedly arises and fades in the system, resulting in auto-oscillations of the surface tension in agreement with the experimental data. The system evolution during the oscillation is discussed in detail. It is established that the presence of a boundary in the radial direction is a necessary precondition for the appearance of the second and following oscillations.

Journal Article↗
PubMed2005

Measurement of harmonic phase differences by interference of attosecond light pulses.

By using a self-referencing technique, we have experimentally measured the influence of the carrier-envelope phase of femtosecond light pulses on the phase of the electric field of the radiation produced by high-order harmonic generation. We show that, in particular experimental conditions, the temporal evolution of the electric field of the attosecond pulses, is directly controlled by the carrier-envelope phase of the driving pulses.

Journal Article↗
PubMed1978

Behavioral marriage therapy. III. The contents of Gurman et al. may be hazardous to our health.

This paper was written as a reply to a critique of behavioral marital therapy (BMT) by Gurman, Kniskern, and Knudson (6, 7). The reply is divided into four sections. First, the paper addresses the critics' comments on the conceptual model put forth by BMT, correcting and clarifying various misconceptions, and restating some of the basic ideological principles in the behavioral model. Second, the paper discusses behavioral change techniques and technology, along with extratechnological treatment considerations. Again, misrepresentations of BMT are corrected. Third, an analysis of the literature investigating the therapeutic efficacy of BMT is reviewed, and the conclusion is reached that BMT is demonstrably effective, at least for a substantial number of mildly to moderately distressed couples. Criticisms are made of the analysis of the same literature conducted by Gurman et al. We conclude that, contrary to the spirit of the paper by Gurman et al., BMT is a viable framework for conceptualizing and treating relationship problems and that the commitment of its adherents to experimental investigation promises continued evolution, refinement, and improvement.

Behavior Therapy↗
PubMed2005

Influence of alcohol in mouthwashes containing triclosan and zinc: an experimental gingivitis study.

OBJECTIVES: An experimental gingivitis model was used to analyse the influence of alcohol in mouthwashes containing 0.15% triclosan and zinc chloride on the formation of supragingival plaque, the development of gingivitis and the appearance of adverse events. MATERIAL AND METHODS: Using a double-blind crossover design, 30 subjects underwent two consecutive experimental phases with two 0.15% triclosan and zinc chloride mouthwashes, differentiated mainly by their excipient (hydroalcoholic or aqueous). In each phase, the subjects discontinued all oral hygiene measures and were treated solely with the randomly assigned experimental mouthwash for 21 days. Each experimental phase was preceded by a 14-day washout period in which, after receiving a complete oral prophylaxis, the subjects were instructed to perform thorough oral hygiene procedures. Gingivitis and plaque levels were assessed at the start and end of both the experimental phases. RESULTS: The evolution of the gingivitis and plaque indices showed no statistically significant differences between both treatments. The mean gingival index increased from 0.30 to 0.38 with the non-alcoholic mouthwash and from 0.32 to 0.42 with the hydroalcoholic mouthwash. The respective changes in plaque index were from 0.88 to 1.93 and from 0.94 to 1.92. The hydroalcoholic mouthwash produced a larger number of fresh symptoms (p=0.033), oral itching being the most reported. CONCLUSIONS: Alcohol does not influence the effectiveness of a 0.15% triclosan and zinc chloride mouthwash against gingivitis development and supragingival plaque formation. The absence of alcohol significantly decreases the incidence of adverse events produced by the mouthwash.

Adolescent↗
PubMed1988

Experimental Escherichia coli endocarditis in rats: roles of serum bactericidal activity and duration of catheter placement.

Studies were undertaken to investigate the relationship of the sensitivity of Escherichia coli to the bactericidal properties of serum and the ability of different strains to induce and sustain endocardial infection in rats. Strains of E. coli demonstrated different degrees of serum sensitivity, as determined by a method which employed concentrations of serum from 10 to 95% and periods of incubation as long as 24 h. The greater the serum sensitivity of the E. coli strain, the less able it was to initiate infection and the more rapidly it was spontaneously eliminated from established infections. Endocardial infection with E. coli was established by intravenous challenge in rats with polyethylene catheters passing through the aortic valve into the left ventricle. An E. coli strain of low serum sensitivity was used; the initiation of infection depended upon the length of time the catheter had been in place and, in addition, whether the catheter was in place at the time of bacterial challenge. Removal of the catheter permitted spontaneous sterilization of the endocardial vegetations. The time necessary for sterilization was in direct proportion to the length of time the catheter remained in place following bacterial challenge. If the catheter was not removed, sterilization of the endocardial vegetations did not take place. These studies suggest that serum bactericidal activity is an important host defense mechanism, acting to prevent the initiation of endocarditis in the case of highly serum-sensitive E. coli and to sterilize experimentally induced endocarditis in the case of less-serum-sensitive bacteria. The catheter used to induce nonbacterial endocardial vegetations favored the colonization of vegetations by E. coli, and it delayed the spontaneous sterilization of infected vegetations which occurred in relation to the susceptibility of the strain to the bactericidal properties of the serum. This effect of the catheter was not attributable to bacteria remaining viable in its lumen, nor was it attributable to inhibition of the bactericidal capacity of the serum as measured in vitro. Whatever the mechanism responsible for the catheter effect, experimental studies of the evolution of infections established with this technique must take into consideration the duration of catheter placement and whether and for how long it was present before or after inoculation with test bacteria.

Animals↗
PubMed2005

Influence of additional active ingredients on the effectiveness of non-alcoholic chlorhexidine mouthwashes: a randomized controlled trial.

BACKGROUND: Non-alcoholic chlorhexidine mouthwashes are equally effective and have fewer potential risks than hydroalcoholic solutions. Nowadays, other active ingredients are added to these mouthwashes in an attempt to improve their effectiveness and reduce side effects. Following an experimental gingivitis model, this study examined three non-alcoholic commercial mouthwashes having 0.12% chlorhexidine digluconate (CHX) in common. METHODS: Using a double masked, cross-over design, 30 subjects underwent three consecutive experimental phases with three mouthwashes: CHX, CHX + 0.05% sodium fluoride (CHXNaF), and CHX + 0.05% cetylpyridinium chloride (CHX-CPC). In each one of these 21-day phases, the subjects discontinued all oral hygiene measures and were treated exclusively with the experimental mouthwash randomly assigned (an oral rinse twice a day). Each experimental phase was preceded by a 14-day washout period. Levels of gingivitis, dental plaque, supragingival calculus, and dental staining were assessed at baseline and end (day 21) of experimental phases. RESULTS: The evolution of gingival and dental staining indices did not show statistically significant differences between the treatments. Differences were noticed in the plaque index (P = 0.0002), with CHX-NaF the treatment with the greatest increase. Differences were also observed in the supragingival calculus index (P = 0.0136), with CHX-CPC showing a smaller increase. Tongue staining was more frequent with CHX-CPC (P = 0.0141). CONCLUSION: In non-alcoholic 0.12% chlorhexidine mouthwashes, the addition of other active ingredients does not produce beneficial effects, but may even reduce the antiplaque effectiveness or increase tongue staining.

Adult↗
PubMed1999

A brief history of medical diagnosis and the birth of the clinical laboratory. Part 1--Ancient times through the 19th century.

From tasting urine to microscopy to molecular testing, the sophistication of diagnostic techniques has come a long way and continues to develop at break-neck speed. The history of the laboratory is the story of medicine's evolution from empirical to experimental techniques and proves that the clinical lab is the true source of medical authority. Part 1 in a 2-part series.

Chronology as Topic↗
PubMed2000

Tibetan and Andean patterns of adaptation to high-altitude hypoxia.

Understanding the workings of the evolutionary process in contemporary humans requires linking the evolutionary history of traits with their current genetics and biology. Unusual environments provide natural experimental settings to investigate evolution and adaptation. The example of high-altitude hypoxia illustrates some of the progress and many of the remaining challenges for studies of evolution in contemporary populations. Current studies exemplify the frequently encountered problem of determining whether large, consistent population differences in mean values of a trait reflect genetic differences. In this review I describe 4 quantitative traits that provide evidence that indigenous populations of the Tibetan and Andean plateaus differ in their phenotypic adaptive responses to high-altitude hypoxia. These 4 traits are resting ventilation, hypoxic ventilatory response, oxygen saturation, and hemoglobin concentration. The Tibetan means of the first 2 traits were more than 0.5 standard deviation higher than the Aymara means, whereas the Tibetan means were more than 1 standard deviation lower than the Aymara means for the last 2 traits. Quantitative genetic analyses of within-population variance revealed significant genetic variance in all 4 traits in the Tibetan population but only in hypoxic ventilatory response and hemoglobin concentration in the Aymara population. A major gene for oxygen saturation was detected among the Tibetans. These findings are interpreted as indirect evidence of population genetic differences. It appears that the biological characteristics of sea-level humans did not constrain high-altitude colonists of the 2 plateaus to a single adaptive response. Instead, microevolutionary processes may have operated differently in the geographically separated Tibetan and Andean populations exposed to the same environmental stress. Knowledge of the genetic bases of these traits will be necessary to evaluate these inferences. Future research will likely be directed toward determining whether the population means reflect differences identified at the chromosomal level. Future research will also likely consider the biological pathways and environmental influences linking genotypes to phenotypes, the costs and benefits of the Tibetan and Andean patterns of adaptation, and the question of whether the observed phenotypes are indeed adaptations that enhance Darwinian fitness.

Adaptation, Physiological↗
PubMed2003

Histomorphometric evaluation of renal glomeruli exposed to sustained delivery of estrogen using adult ovariectomized rats.

Hormonal replacement therapy (HRT) has shown to be efficacious in treatment and preventing of heart disease, osteoporosis and reducing mortality in postmenopausal and ovariectomized females. Several attempts to utilize the native estrogen and its analogs such as Depo-Provera, conjugated estrogen and estrogen benzoate have shown different physiological responses. In addition, the route of administration and its mode of action is lacking in the literature. The specific objective of this study was to investigate the role of sustained delivery of estrogen on the functional and structural capacity of the kidney using adult female rats as a model. A total of 24 adult female rats were subdivided into four equal groups. Groups I and II were ovariectomized (OVX) by following standard laboratory surgical procedures. Each rat in groups II and III (intact) were implanted with tricalcium phosphate lysine (TCPL) drug delivery system loaded with 40 mg of estrogen. Rats in group IV were unimplanted and untreated to be served as a control group. At the end of 45 days post treatment the animals were sacrificed by using overdose of Halothane and assured by cervical dislocation. Vital and reproductive organs were retrieved, weighed and subjected to H&E staining procedure. The results of this investigation suggest: (i) TCPL delivery system released estrogen at a sustained level for 45 days without any untoward response, (ii) the wet weights of kidneys (normalized to body weight) were increased (p < 0.05) in intact rats treated with estrogen compared to control, (iii) sustained delivery of estrogen resulted in a maintenance of kidney weights compared to the control level, however, the lack of estrogen treatment resulted in a remarkable regression in the kidney weights of OVX rats, (iv) the ratio of renal arteries-diameter (normalized to arterial wall thickness) was significantly increased in intact rats treated with estrogen compared to the control and other experimental groups, (v) histopathological evolutions of renal tubules revealed tubular epithelial damage in intact rats received estrogen treatment compared to the control and other groups. In conclusion, this study suggests that exogenous estrogen therapy could lead profound tubular damage and consequently major renal insufficiency. HRT also could lead to hypertensive renal damage.

Animals↗
PubMed1979

[Experimental hepatic encephalopathy. The effect of portocaval shunt on the evolution of the anterior hypothalamic neurosecretion in the rat (author's transl)].

The evolution of the anterior hypothalamic neurosecretion is studied in control, sham-operated and portocaval shunt rats. In sham-operated related to control rats, no modification of the anterior hypothalamic neurosecretion is observed. In portocaval shunt rats, the hypothalamic neurosecretion increases. This increase is mainly observed into the median eminence in all the portocaval shunt rats. The hypothesis according to which the modification of neurosecretory acitivity of the hypothalamic structures may be related to a discrepancy between the central monoamines is discussed.

Animals↗