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At least 163 records · Page 9Linked to original sources
PubMed1985

Steady-state kinetic analysis of transcription of cloned tRNASer genes from Drosophila melanogaster.

Drosophila melanogaster Schneider II cells contain a factor which inhibits transcription in vitro of cloned tRNA genes in crude extracts made from these cells. The inhibitor could, however, be effectively neutralized by addition of certain non-template DNAs. In the absence of the transcription inhibitor activity, the steady-state kinetics of tRNA production from cloned genes followed one-substrate enzyme kinetics to a high degree of accuracy. Maximal rates of transcription and apparent affinity constants were analyzed for a collection of cloned D. melanogaster tRNASer genes. The stability of the complex formed by the transcription proteins and the template DNA was found to be nearly constant for the genes examined. The transcription rates, however, were greatly influenced by the DNA sequences flanking the tRNA genes. Analysis of transcription competition between DNA templates showed pure competitive behavior. Inhibition constants derived from these experiments indicated that the formation of the transcription complex was affected by sequences flanking the tRNA genes. Furthermore, the rate-limiting step in complex formation was independent of the stability of the final form of the complex.

Cloning, Molecular↗
PubMed1995

Privatization and just healthcare.

When advocates of insurance-privatization consider whether private insurance-dominated systems achieve justice at all, they tend to rely on an incomplete set of criteria for a just healthcare system. They also mistakenly assume that it is enough to show that justice is in principle achievable within a private insurance-dominated system. This essay offers a more complete set of criteria for a just healthcare system. It then argues that the motivational assumptions needed to make insurance-privatization at all plausible (on grounds of choice, efficiency, and quality of care) are inconsistent with the motivational assumptions needed to show that in practice a private insurance-dominated system will achieve justice. A private insurance-dominated system can be expected to satisfy the criteria for just healthcare only if (a) there is extensive and effective regulation to constrain the normal competitive behavior of private insurers or if (b) generous public funds are provided to fill the gaps in access left by the private insurance market. Yet the assumptions about the motivations and abilities of the public, regulators, and public officials needed to satisfy conditions (a) or (b) contradict the privatization advocate's explanations of how privatization will maximize efficiency, choice, and quality of care.

Altruism↗
PubMed1986

Effects of Ca2+ channel blockers on Ca2+ translocation across synaptosomal membranes.

The binding of [3H]nimodipine to purified synaptic plasma membranes (SPM) isolated from sheep brain cortex was characterized, and the effects of nimodipine, nifedipine, and (+)-verapamil on the [3H]nimodipine binding were compared to the effects on 45Ca2+ translocation under conditions that separate 45Ca2+ fluxes through Ca2+ channels from 45Ca2+ uptake via Na+/Ca2+ exchange. [3H]Nimodipine labels a single class of sites in SPM, with a KD of 0.64 +/- 0.1 nM, a Bmax of 161 +/- 27 fmol X mg-1 protein, and a Hill slope of 1.07, at 25 degrees C. Competition of [3H]nimodipine binding to purified SPM with unlabelled Ca2+ channel blockers shows that: nifedipine and nimodipine are potent competitors, with IC50 values of 4.7 nM and 5.9 nM, respectively; verapamil and (-)-D 600 are partial competitors, with biphasic competition behavior. Thus, (+)-verapamil shows an IC50 of 708 nM for the higher affinity component and the maximal inhibition is 50% of the specific binding, whereas for (-)-verapamil the IC50 is 120 nM, and the maximal inhibition is 30%; (-)-D 600 is even less potent than verapamil in inhibiting [3H]nimodipine binding (IC50 = 430 nM). However, (+)-verapamil, nifedipine, and nimodipine are less potent in inhibiting depolarization-induced 45Ca2+ influx into synaptosomes in the absence of Na+/Ca2+ exchange than in competing for [3H]nimodipine binding. Thus, (+)-verapamil inhibits Ca2+ influx by 50% at about 500 microM, whereas it inhibits 50% of the binding at concentrations 200-fold lower, and the discrepancy is even larger for the dihydropyridines. The Na+/Ca2+ exchange and the ATP-dependent Ca2+ uptake by SPM vesicles are also inhibited by the Ca2+ channel blockers verapamil, nifedipine, and d-cis-diltiazem, with similar IC50 values and in the same concentration range (10(-5)-10(-3) M) at which they inhibit Ca2+ influx through Ca2+ channels. We conclude that high-affinity binding of the Ca2+ blockers by SPM is not correlated with inhibition of the Ca2+ fluxes through channels in synaptosomes under conditions of minimal Na+/Ca2+ exchange. Furthermore, the relatively high concentrations of blockers required to block the channels also inhibit Ca2+ translocation through the Ca2+-ATPase and the Na+/Ca2+ exchanger. In this study, clear differentiation is made of the effects of the Ca2+ channel blockers on these three mechanisms of moving Ca2+ across the synaptosomal membrane, and particular care is taken to separate the contribution of the Na+/Ca2+ exchange from that of the Ca2+ channels under conditions of K+ depolarization.

Adenosine Triphosphatases↗
PubMed1976

A behavioral classification of welfare children from survey data.

From survey data on 1000 urban Welfare AFDC children aged six to eighteen, a hierarchical cluster analysis yielded six distinct behavioral types of Welfare children. Characteristics of each type, and its relationship to treatment, ethnicity, and other variables are discussed. Advantages of this system of behavioral classification for research and population assessment are outlined.

Achievement↗
PubMed1995

Early Interactions of Rhizobium leguminosarum bv. phaseoli and Bean Roots: Specificity in the Process of Adsorption and Its Requirement of Ca(sup2+) and Mg(sup2+) Ions.

Roots of Phaseolus vulgaris L. were incubated with dilute suspensions (1 x 10(sup3) to 3 x 10(sup3) bacteria ml(sup-1)) of an antibiotic-resistant indicator strain of Rhizobium leguminosarum bv. phaseoli in mineral medium and washed four times by a standardized procedure prior to quantitation of adsorption (G. Caetano-Anolles and G. Favelukes, Appl. Environ. Microbiol. 52:371-376, 1986). The population of rhizobia remaining adsorbed on roots after washing was homogeneous, as indicated by the first-order course of its desorption by hydrodynamic shear. Rhizobia were maximally active for adsorption in the early stationary phase of growth. The process leading to adsorption was rapid, without an initial lag, and slowed down after 1 h. Adsorption of the indicator strain at 10(sup3) bacteria ml(sup-1) was inhibited to different extents in the presence of 10(sup3) to 10(sup8) antibiotic-sensitive competitor rhizobia ml(sup-1). After a steep rise above 10(sup4) bacteria ml(sup-1), inhibition by heterologous competitors in the concentration range of 10(sup5) to 10(sup7) bacteria ml(sup-1) was markedly less than by homologous strains, while at 10(sup8) bacteria ml(sup-1) it approached the high level of inhibition by the latter. At 10(sup7) bacteria ml(sup-1), all of the heterologous strains tested were consistently less inhibitory than homologous competitors (P < 0.001). These differences in competitive behavior indicate that in the process of adsorption of R. leguminosarum bv. phaseoli to its host bean roots, different modes of adsorption occur and that some of these modes are specific for the microsymbiont (as previously reported for the alfalfa system [G. Caetano-Anolles and G. Favelukes, Appl. Environ. Microbiol. 52:377-381, 1986]). Moreover, whereas the nonspecific process occurred either in the absence or in the presence of Ca(sup2+) and Mg(sup2+) ions, expression of specificity was totally dependent on the presence of those cations. R. leguminosarum bv. phaseoli bacteria adsorbed in the presence of Ca(sup2+) and Mg(sup2+) were more resistant to desorption by shear forces than were rhizobia adsorbed in their absence. These results indicate that (i) symbiotic specificity in the P. vulgaris-R. leguminosarum bv. phaseoli system is expressed already during the early process of rhizobial adsorption to roots, (ii) Ca(sup2+) and Mg(sup2+) ions are required by R. leguminosarum bv. phaseoli for that specificity, and (iii) those cations cause tighter binding of rhizobia to roots.

Journal Article↗
PubMed2005

Competitive dynamics in cortical responses to visual stimuli.

Neurons in the visual cortex of the macaque monkey exhibit a variety of competitive behaviors, including normalization and oscillation, when presented with multiple visual stimuli. Here we argue that a biophysically plausible cortical circuit with opponent inhibition, spike-frequency adaptation, and synaptic depression can account for the full range of behaviors. The governing parameter is the strength of inhibition between competing neuronal pools. As the strength of inhibition is increased, the pattern of network behavior shifts from normalization mode to oscillatory mode, with oscillations occurring at progressively lower frequency until, at the extreme, winner-take-all behavior appears.

Action Potentials↗
PubMed2006

Time course of oculomotor inhibition revealed by saccade trajectory modulation.

Selecting a stimulus as the target for a goal-directed movement involves inhibiting other competing possible responses. Both target and distractor stimuli activate populations of neurons in topographic oculomotor maps such as the superior colliculus. Local inhibitory interconnections between these populations ensure only one saccade target is selected. Suppressing saccades to distractors may additionally involve inhibiting corresponding map regions to bias the local competition. Behavioral evidence of these inhibitory processes comes from the effects of distractors on oculomotor and manual trajectories. Individual saccades may initially deviate either toward or away from a distractor, but the source of this variability has not been investigated. Here we investigate the relation between distractor-related deviation of trajectory and saccade latency. Targets were presented with, or without, distractors, and the deviation of saccade trajectories arising from the presence of distractors was measured. A fixation gap paradigm was used to manipulate latency independently of the influence of competing distractors. Shorter-latency saccades deviated toward distractors and longer-latency saccades deviated away from distractors. The transition between deviation toward or away from distractors occurred at a saccade latency of around 200 ms. This shows that the time course of the inhibitory process involved in distractor related suppression is relatively slow.

Fixation, Ocular↗
PubMed2006

Developing a center for comparative effectiveness information.

Interest in objective, credible comparative clinical effectiveness information has been growing in the United States, both by those who support competitive behavior in health care and by those who support administered pricing. The Medicare drug benefit has heightened interest in better information, although the potential payoff is even greater for medical procedures than for drugs, since procedures account for more of the health care dollar. Careful consideration needs to be given regarding the appropriate structure, placement, financing, and function of an agency devoted to comparative effectiveness if it is to achieve its objective: a mechanism to support better decision making in health care.

Cost-Benefit Analysis↗
PubMed2002

Human group choice: discrete-trial and free-operant tests of the ideal free distribution.

Ideal free distribution theory predicts that foragers will form groups proportional in number to the resources available in alternative resource sites or patches, a phenomenon termed habitat matching. Three experiments tested this prediction with college students in discrete-trial simulations and a free-operant simulation. Sensitivity to differences in programmed reinforcement rates was quantified by using the sensitivity parameter of the generalized matching law (s). The first experiment, replicating prior published experiments, produced a greater degree of undermatching for the initial choice (s = 0.59) compared to final choices (s = 0.86). The second experiment, which extended prior findings by allowing only one choice per trial, produced comparable undermatching (s = 0.82). The third experiment used free-operant procedures more typical of laboratory studies of habitat matching with other species and produced the most undermatching (s = 0.71). The results of these experiments replicated previous results with human groups, supported predictions of the ideal free distribution, and suggested that undermatching represents a systematic deviation from the ideal free distribution. These results are consistent with a melioration account of individual behavior as the basis for group choice.

Adolescent↗
PubMed1991

An expanded function for superoxide dismutase.

alpha-Hydroxyalkylperoxyl radicals were generated from the primary and secondary alcohols methanol, ethanol and 2-propanol in N2O/O2-saturated aqueous solutions by pulse radiolysis. These radicals reduced a ferric iron porphyrin complex, tetrakis-(4-N-methylpyridyl)porphine, with diffusion-controlled rate constants. The extreme sensitivity of the shift of the Soret absorption band in this reaction was used to determine, by competition kinetics, the reactivity of the peroxyl radicals with different proteins. Only native Cu,Zn-superoxide dismutase and metallothionein showed competitive behavior, with SOD exhibiting rate constants close to the dismutation rate for O2-. Metallothionein was slower by a factor of 30 with hydroxymethylperoxyl radicals. We propose, that SOD has unique properties of the protein surface in addition to the prosthetic copper site, having possibly evolved as a 'general-purpose radical-scavenging protein'.

Alcohols↗
PubMed2006

Using Theraplay in shelter settings with mothers & children who have experienced violence in the home.

This article describes a group program for women and children exposed to violence in the home. The program is primarily based on Theraplay, an attachment-based intervention approach for working with both adults and children who have a variety of emotional and behavioral difficulties. The theoretical and research bases, as well as the guiding principles of Theraplay, will be outlined and discussed, and the rationale for its application to a shelter setting will be highlighted. Finally, the benefits of and challenges to implementing such a program and the implications for practice and further evaluation will be explored.

Adult↗
PubMed2001

Short-term dynamics of relative coordination between respiratory movements, heart rate and arterial pressure fluctuations within the respiratory frequency range.

The possible linear short-term coordination between respiratory movements (RESP), heart rate fluctuations (HRF), and arterial blood pressure fluctuations (BPF) in conscious human beings has not yet been investigated because of the restricted time resolution of conventional time series analysis. At present, this short-term dynamics as an expression of relative coordination can be quantified by newly developed adaptive autoregressive modeling of time series using Kalman filtering. Thus, in 6 conscious healthy volunteers, RESP, HRF, and BPF were recorded during 10 min in the supine position, at rest and during paced breathing. A considerable part of calculated ordinary and partial coherence sequences of short-term resolution between RESP and HRF, RESP and BPF, and partially between HRF and BPF showed patterns varying in time that could be correlated to changes between gradual coordinations (coherence changing between 0.40 and 0.95). They were more seldom complete or absent. There were mostly opposite changes between partial coherence sequences RESP-HRF/BPF and RESP-BPF/HRF demonstrating competitive behavior between these coordinations. Paced breathing did not essentially affect any observed characteristics. Therefore, these coherence dynamics are not essentially dependent on voluntary breathing movements. We conclude that to a different extent these linear and changing couplings between RESP, HRF, and BPF in conscious human beings exhibit properties of short-term complete and more frequently gradual coordinations showing dynamics that can not be determined by conventional methods.

Adult↗
PubMedDate not supplied

The effects of food presentation and microhabitat upon resource monopoly in a ground-foraging ant (Hymenoptera: Formicidae) community.

In Neotropical wet forests several species of omnivorous, resource-defending ants, live and forage in close proximity to one another. Although the forest floor is heterogeneous in microhabitat and food quantity, little is known about the impact of microhabitat and food variation upon resource monopoly among ants. We investigated how food type and microhabitat influence food monopoly in resource-defending ants in old-growth tropical wet forest in the Caribbean lowlands of Costa Rica. We measured several microhabitat characteristics at 66 points in a 0.5 hectare plot, and baited each point with two categories of tuna bait. These baits were presented in "split" and "clumped" arrangements. We measured the frequency of bait monopoly by a single species, as well as the number of recruited ant foragers at a bait. Out of five common species, two (Wasmannia auropunctata and Pheidole simonsi) more frequently monopolized one bait type over the other, and one (P. simonsi) recruited more ants to the split baits. We then considered the recruitment response by all ant species in the community. We found that the frequency of monopoly, sharing, and the absence of ants at a given point in the rainforest differed with bait type. The frequency of monopoly was associated with microhabitat type in two out of eight microhabitat variables (leaf litter depth and palms); variation in two other types (canopy tree distance and leafcutter ant trails) was associated with changes in forager number. In at least two ant species, food presentation affected monopoly at baits; among all resource-defending ants, the microhabitats where ants foraged for food and the type of food located determined in part the frequency of monopoly and the number of foragers at the food item. These results suggest that the location and presentation of food items determines in part which ant species will utilize the resource.

Animals↗
PubMed2003

The mumpsimus.

It is an unfortunate side of human nature, on occasion, to stubbornly refuse to change our minds or listen to evidence that challenges our beliefs. In the extreme form, such individuals are called mumpsimuses. This column describes what research has been able to tell us about why individuals continue to escalate their commitments to failing causes and why beliefs are so resistant to change, even in the light of reason. In fact, it is usually best to leave a sleeping mumpsimus lie.

Attitude↗