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PubMed1996

Taste responses to binary mixtures of amino acids in the sea catfish, Arius felis.

In vivo electrophysiological recordings in the sea catfish, Arius felis, showed that the magnitude of the integrated facial taste responses to binary mixtures of amino acids was predictable with knowledge obtained from previous cross-adaptation studies of the relative independence of the respective binding sites of the component stimuli. Each component from which equal aliquots were drawn to form the mixtures was adjusted in concentration to provide for approximately equal response magnitudes. The magnitude of the taste responses to binary mixtures whose component amino acids showed minimal cross-adaptation was significantly greater than that to binary mixtures whose components exhibited considerable cross-reactivity. There was no evidence for mixture suppression. The relative magnitude of the taste responses in the sea catfish to stimulus mixtures is similar to that previously reported for olfactory receptor responses in the freshwater channel catfish and chorda tympani taste responses in the hamster.

Amino Acids↗
PubMed1998

Effects of context on judgements of odor intensities in humans.

This study evaluated whether the intensity of previously smelled odors could unintentionally influence the subsequent judgement of odor intensity. The predicted context effect was based on the adaptation-level theory. Before and 25 min after either WEAK or STRONG biasing odor concentrations, 51 subjects were required to rate the intensity of 10 different odor concentrations of California Orange Oil. After the WEAK bias, subjects judged the odor intensity as being stronger than they did after the STRONG bias. Thus the intensity of odors smelled 25 min earlier can unintentionally influence subsequent odor intensity judgement. The findings are discussed in the light of two alternative explanations, namely, a central implicit memory process and a stimulus-level-based change at the peripheral level.

Adolescent↗
PubMed2022

Analysis of nested alternate open reading frames and their encoded proteins.

Transcriptional and post-transcriptional mechanisms diversify the proteome beyond gene number, while maintaining a sequence relationship between original and altered proteins. A new mechanism breaks this paradigm, generating novel proteins by translating alternative open reading frames (Alt-ORFs) within canonical host mRNAs. Uniquely, 'alt-proteins' lack sequence homology with host ORF-derived proteins. We show global amino acid frequencies, and consequent biochemical characteristics of Alt-ORFs nested within host ORFs (nAlt-ORFs), are genetically-driven, and predicted by summation of frequencies of hundreds of encompassing host codon-pairs. Analysis of 101 human nAlt-ORFs of length ≥150 codons confirms the theoretical predictions, revealing an extraordinarily high median isoelectric point (pI) of 11.68, due to anomalous charged amino acid levels. Also, nAlt-ORF proteins exhibit a >2-fold preference for reading frame 2 versus 3, predicted mitochondrial and nuclear localization, and elevated codon adaptation index indicative of natural selection. Our results provide a theoretical and conceptual framework for exploration of these largely unannotated, but potentially significant, alternative ORFs and their encoded proteins.

Journal Article↗
PubMedDate not supplied

Ecotypic differentiation of gas exchange responses and leaf anatomy in a tropical forest understory shrub from areas of contrasting rainfall regimes.

Many studies have documented genetic differentiation of physiological ecotypes along environmental gradients in the temperate zone, but this topic has received little attention in tropical plants. We collected cuttings of Psychotria horizontalis (Rubiaceae) from Atlantic and Pacific coastal areas in central Panama, which differed twofold in annual rainfall, and grew them under common conditions in a screened, open-air growing house for 14 months. Plants from the wetter (Atlantic) region showed significantly higher stomatal conductance, but photosynthetic rates were similar in both groups, leading to higher water use efficiency in plants from the drier (Pacific) region. Responses of stomatal conductance to atmospheric humidity were similar in both groups. Anatomical studies show that plants from the wetter region had a higher mesophyll surface area per unit leaf area (A(mes)/A(leaf)) than plants from the drier region (17.2 versus 13.9), and also had a higher stomatal density (161.5 versus 98.0 mm(-2)) and fewer trichomes (2.0 versus 18.7 mm(-2)). The proportion of palisade cell surface area that was exposed to intercellular airspaces is higher in plants from the Pacific coast than from the Atlantic coast, such that the total palisade cell surface area exposed to the intercellular airspaces is similar in plants from the two regions (A(mes)/A(leaf) = 1.7). Paired plants transplanted into natural forest understory conditions showed considerable variability among sites, but plants from the drier region consistently had lower stomatal conductance than plants from the wetter region. After 20 months in the field, plant growth was similar regardless of plant origin, but plants of Pacific coast origin had longer roots and more (but smaller) leaves than plants of Atlantic coast origin. Stomatal density in field-grown plants was higher in plants of Atlantic (135.9 mm(-2)) than Pacific (90.1 mm(-2)) origin. An understanding of genetically based adaptations to local environmental conditions is important for predicting the consequences of climatic change and forest fragmentation.

Journal Article↗
PubMed2000

Female control of paternity in the sexually cannibalistic spider Argiope keyserlingi.

Sexual conflict theory predicts an antagonistic coevolution, with each sex evolving adaptations and counter-adaptations to overcome a temporary dominance of the other sex over the control of paternity. Polyandry allows sexual selection to operate after mating has commenced, with male and female interests competing for control of fertilization. There are numerous examples of male control of paternity, but few studies have unambiguously revealed female control. Attributing variance in paternity to females is often difficult since male and female influences cannot be separated unambiguously. However, we show that polyandrous female orb-web spiders Argiope keserlingi (Arancidae) control the paternity of their offspring by adjusting the timing of sexual cannibalism. Our experiments reveal that females copulating with relatively smaller males delay sexual cannibalism, thereby prolonging the duration of copulation, and that these males consequently fertilize relatively more eggs.

Animals↗
PubMed2006

Dynamics of vascular branching morphogenesis: the effect of blood and tissue flow.

Vascularization of embryonic organs or tumors starts from a primitive lattice of capillaries. Upon perfusion, this lattice is remodeled into branched arteries and veins. Adaptation to mechanical forces is implied to play a major role in arterial patterning. However, numerical simulations of vessel adaptation to haemodynamics has so far failed to predict any realistic vascular pattern. We present in this article a theoretical modeling of vascular development in the yolk sac based on three features of vascular morphogenesis: the disconnection of side branches from main branches, the reconnection of dangling sprouts ("dead ends"), and the plastic extension of interstitial tissue, which we have observed in vascular morphogenesis. We show that the effect of Poiseuille flow in the vessels can be modeled by aggregation of random walkers. Solid tissue expansion can be modeled by a Poiseuille (parabolic) deformation, hence by deformation under hits of random walkers. Incorporation of these features, which are of a mechanical nature, leads to realistic modeling of vessels, with important biological consequences. The model also predicts the outcome of simple mechanical actions, such as clamping of vessels or deformation of tissue by the presence of obstacles. This study offers an explanation for flow-driven control of vascular branching morphogenesis.

Animals↗
PubMed2002

Forgetting to remember: the functional relationship of decay and interference.

Functional decay theory proposes that decay and interference, historically viewed as competing accounts of forgetting, are instead functionally related. The theory posits that (a) when an attribute must be updated frequently in memory, its current value decays to prevent interference with later values, and (b) the decay rate adapts to the rate of memory updates. Behavioral predictions of the theory were tested in a task-switching paradigm in which memory for the current task had to be updated every few seconds, hundreds of times. Reaction times and error rates both increased gradually between updates, reflecting decay of memory for the current task. This performance decline was slower when updates were less frequent, reflecting a decrease in the decay rate following a decrease in the update rate. A candidate mechanism for controlled decay is proposed, the data are reconciled with practice effects, and implications for models of executive control are discussed.

Humans↗
PubMed2007

Herbivore-induced plant volatiles as cues for habitat assessment by a foraging parasitoid.

1. Animals usually require information about the current state of their habitat to optimize their behaviour. For this, they can use a learning process through which their estimate is continually updated according to the cues they perceive. Identifying these cues is a long-standing but still inveterate challenge for ecologists. 2. The use of plant cues by aphid parasitoids for the assessment of habitat profitability and the adaptation of patch exploitation was studied. Grounding on predictions from optimal foraging theory, we tested whether parasitoids exploited host patches less intensively after visiting heavily infested plants than after visiting plants bearing fewer aphids. 3. As predicted, after visiting heavily infested plants parasitoids reduced their residence time and attacked fewer hosts in the next patch. This was the case regardless of whether the aphids were actually present on the first plant, indicating that the cue came from the plant. Moreover, the level of infestation of a plant at some distance from the first plant visited affected parasitoid patch exploitation on the second plant in a similar manner, indicating that the cue was volatile. 4. These results highlight a novel role of herbivore-induced volatiles in parasitoid foraging behaviour, different from the widely studied attraction at a distance.

Animals↗
PubMed2004

Virtual sensing for broadband noise control in a lightly damped enclosure.

Available virtual sensing schemes either depend on assumptions that are valid for isolated frequencies, or require heavy online adaptations. A simple method is proposed here to predict the virtual signal exactly for broadband noise control in a lightly damped enclosure. The proposed method requires two physical sensors installed judiciously in a sound field to predict a virtual signal. The method is based on an exact mathematical relation between the virtual and physical sensors, which is valid for the entire frequency of interest. It is possible to use multiple sensor-pairs to reduce the sensitivity of the proposed method with respect to acoustic parameters, such as speed of sound or sensor mismatching. Experimental results are presented to verify the analytical results.

Acoustics↗
PubMed1983

Biodegradation and photolysis of pentachlorophenol in artificial freshwater streams.

The biodegradation, photolysis, and adsorption of pentachlorophenol (PCP) in outdoor, aquatic environments were examined with man-made channels built by the U.S. Environmental Protection Agency at a field station on the Mississippi River near Monticello, Minn. Four channels were used, each channel being approximately 520 m long and receiving river water that flowed through the channels for about 10 h before reentering the river. The channels were dosed continuously during the summer of 1982 with various concentrations of PCP (approximately 0, 48, 144, and 432 micrograms/liter). We monitored the biotic and abiotic degradation of PCP in these channels for approximately 16 weeks. Photolysis of PCP was rapid at the water surface, but greatly attenuated with depth. Depending on sunlight conditions, photolysis accounted for a 5 to 28% decline in initial PCP concentration. Adsorption of PCP by sediment and uptake by biota accounted for less than 15% and probably less than 5% in unacclimated water. Microbial degradation of PCP became significant about 3 weeks after the initiation of dosing and eventually became the primary mechanism of PCP removal, accounting for a 26 to 46% (dose-dependent) decline in initial PCP. Most of the PCP-mineralizing microorganisms that developed in the channels were either attached to surfaces (e.g., rocks and macrophytes) or associated with surface sediments. Total bacterial numbers (direct microscopic counts) in the various channels were not affected significantly by PCP concentrations of micrograms per liter. Numerous strains of bacteria able to grow at the expense of PCP were isolated from the adapted channels. The experiments reported here will help predict the responses of flowing aquatic ecosystems to contamination by biocides such as pentachlorophenol.

Adsorption↗
PubMed2026

The catheterized urinary tract selects for MRR1-mediated efflux and fluconazole resistance in Candida albicans biofilms.

Catheter-associated urinary tract infections (CAUTIs) are the most common nosocomial infection in developed countries, and Candida species are among the most frequently isolated organisms. Despite this, little is known about the biology, host-pathogen interactions, or outcomes of these infections, and this has led to uncertain guidelines for clinical management of Candida CAUTIs. Here, we develop the first physiologically relevant artificial urine medium (AUM) that supports fungal growth in a manner similar to, but more consistent than, human urine samples. We demonstrate that human catheter-associated (CA) clinical isolates of C. albicans exhibit environment-dependent fluconazole resistance: many isolates determined to be susceptible by standard CLSI testing in RPMI (MIC ≤ 2 µg/mL) were fully resistant (MIC ≥ 128 µg/mL) when grown in pooled human urine or AUM, complicating clinical management, which is based on catheter exchange and fluconazole treatment. Transcriptomic profiling of biofilms formed in AUM revealed a remarkably convergent upregulation of efflux and detoxification processes across clinical isolates with diverse biofilm phenotypes. Whole-genome sequencing of the CA isolates identified variant alleles of transcriptional regulators of drug efflux, including MRR1, that have been previously associated with antifungal resistance. A competition assay confirmed that Mrr1 provides a fitness advantage in urine and AUM in a urea-dependent manner. Thus, we show that the urinary environment promotes a unique biofilm differentiation program and selects for adaptations that increase drug resistance and would be predicted to render standard treatment regimens ineffective.IMPORTANCECatheter-associated urinary tract infections are the most common nosocomial infection in the United States, and Candida albicans is one of the most frequently isolated organisms from these infections. Despite this high prevalence, few molecular studies have examined C. albicans biology in the urinary environment, and recommendations for clinical management lack robust evidence. Here, we show that clinical catheter-associated isolates of C. albicans identified as susceptible to fluconazole by standard clinical microbiology testing were resistant when grown in human or artificial urine. We identified transcriptional responses intrinsic to the urinary environment that produce this environment-specific resistance phenotype. Biofilm growth in the urinary environment induces cellular processes for efflux and detoxification. These findings suggest that standard susceptibility testing may not predict fluconazole efficacy in the urinary tract and underscore the need for niche-informed approaches to antifungal management of these common infections.

Candida albicans↗
PubMed2004

Patient preferences for treatment of rheumatoid arthritis.

OBJECTIVE: To elicit treatment preferences of patients with rheumatoid arthritis (RA) for disease modifying antirheumatic drugs (DMARDs) with varying risk profiles. METHODS: Patient values for 16 DMARD characteristics were ascertained using published data about side effects, effectiveness, and cost. Patient preferences were determined by Adaptive Conjoint Analysis, an interactive computer program that predicts preferences by asking patients to make trade-offs between specific treatment characteristics. Simulations were run to derive preferences for four drugs: methotrexate, gold, leflunomide, and etanercept, under different risk-benefit scenarios. Infliximab was not included because it is given with methotrexate, and we did not include preferences for combination therapy. Based on each patient's expressed preferences, and the characteristics of the treatments available at the time of the study, the option that best fitted each patient's perspective was identified. RESULTS: 120 patients (mean age 70 years) were interviewed. For the base case scenario (which assumed the maximum benefits reported in the literature, a low probability of adverse effects, and low equal monthly "co-pays" (out of pocket costs)), 95% of the respondents preferred etanercept over the other treatment options. When all four options were described as being equally effective, 88% continued to prefer etanercept owing to its safer short term adverse effect profile. Increasing etanercept's co-pay to $30.00 decreased the percentage of patients preferring this option to 80%. CONCLUSIONS: In this study, older patients with RA, when asked to consider trade-offs between specific risk and benefits, preferred etanercept over other treatment options. Preference for etanercept is explained by older patients' risk aversion for drug toxicity.

Adult↗
PubMed2007

Validity of an adaptation of the Framingham cardiovascular risk function: the VERIFICA Study.

BACKGROUND: To assess the reliability and accuracy of the Framingham coronary heart disease (CHD) risk function adapted by the Registre Gironí del Cor (REGICOR) investigators in Spain. METHODS: A 5-year follow-up study was completed in 5732 participants aged 35-74 years. The adaptation consisted of using in the function the average population risk factor prevalence and the cumulative incidence observed in Spain instead of those from Framingham in a Cox proportional hazards model. Reliability and accuracy in estimating the observed cumulative incidence were tested with the area under the curve comparison and goodness-of-fit test, respectively. RESULTS: The Kaplan-Meier CHD cumulative incidence during the follow-up was 4.0% in men and 1.7% in women. The original Framingham function and the REGICOR adapted estimates were 10.4% and 4.8%, and 3.6% and 2.0%, respectively. The REGICOR-adapted function's estimate did not differ from the observed cumulated incidence (goodness of fit in men, p = 0.078, in women, p = 0.256), whereas all the original Framingham function estimates differed significantly (p<0.001). Reliabilities of the original Framingham function and of the best Cox model fit with the study data were similar in men (area under the receiver operator characteristic curve 0.68 and 0.69, respectively, p = 0.273), whereas the best Cox model fitted better in women (0.73 and 0.81, respectively, p<0.001). CONCLUSION: The Framingham function adapted to local population characteristics accurately and reliably predicted the 5-year CHD risk for patients aged 35-74 years, in contrast with the original function, which consistently overestimated the actual risk.

Adult↗
PubMed1994

Predictive control of nonlinear systems based on identification by backpropagation networks.

Using the property of universal approximation of multilayer perceptron neural network, a class of discrete nonlinear dynamical systems are modeled by a perceptron with two hidden layers. A backpropagation algorithm is then used to train the model to identify the nonlinear systems to a desired level of accuracy. Based on the identified model, a one-step-ahead predictive control scheme is proposed in which the future control inputs are obtained through some nonlinear optimization process. Making use of the online learning properties of neural networks, the predictive control scheme is further developed into an adaptive one which is robust to the incompleteness of identification. Simulation results show that this neural control scheme works well even for some very complicated nonlinear systems.

Mathematics↗
PubMed1982

Infant birth weight is related to maternal arterial oxygenation at high altitude.

Infant birth weight is reported to decrease at high altitude as a reulst of fetal growth retardation (McCullough, Reeves, and Liljegren. Arch. Environ, Health. 32: 36--39, 1977) but not all babies born at high altitude are small. We hypothesized that maternal characteristics acting to lower arterial O2 content would contribute to smaller infant birth weight. To test this hypothesis, we measured arterial oxygenation serially during pregnancy and again postpartum in 44 residents of Leadville, CO (elevation 3,100 m). We identified three maternal characteristics--ventilation, hemoglobin concentration, and smoking habits--that were related to the birth weight of the offspring. Mothers of smaller babies (less than 2,900 g) compared to mothers of larger babies (greater than 3,500 g) were characterized by hypoventilation, no change or a decrease in ventilation and arterial O2 saturation from early to late gestation, and a falling hemoglobin concentration that combined to lower arterial O2 content in the 3rd trimester. Maternal smoking at 3,100 m was associated with a two to threefold greater reduction in infant birth weight (-546 g) than reported from sea level. Thus, maternal arterial oxygenation during pregnancy may be important for predicting fetal growth retardation and the process of adaptation to high altitude.

Adaptation, Physiological↗
PubMed2001

Coronary artery calcification in older adults to age 99: prevalence and risk factors.

BACKGROUND: Coronary artery calcification has been proposed as a noninvasive method to assess cardiovascular disease (CVD) risk. However, the prevalence and risk factors for coronary artery calcification in populations >65 years have not been well studied. METHODS AND RESULTS: Electron beam tomography was performed to assess coronary artery calcium (CAC) in 614 older adults aged, on average, 80 years (range, 67 to 99 years); 367 (60%) were women, and 143 (23%) were black. Calcium scores ranged from 0 to 5459. Median scores were 622 for men and 205 for women. Scores increased by age and were lower in blacks than in whites. Nine percent of subjects (n=57) had no CAC, and 31% (n=190) had a score lower than 100. A history of CVD was associated with calcium score. Age, male sex, white race, CVD, triglyceride level, pack-years of smoking, and asthma, emphysema, or bronchitis (chronic obstructive pulmonary disease) were independently associated with CAC score in the fourth quartile. CONCLUSIONS: A wide range of CAC scores was observed, suggesting adaptation with aging. CAC may have potential to predict CVD in older adults, but this remains to be determined.

Age Distribution↗
PubMed2001

Mammalian photoperiodic system: formal properties and neuroendocrine mechanisms of photoperiodic time measurement.

Photoperiodism is a process whereby organisms are able to use both absolute measures of day length and the direction of day length change as a basis for regulating seasonal changes in physiology and behavior. The use of day length cues allows organisms to essentially track time-of-year and to "anticipate" relatively predictable annual variations in important environmental parameters. Thus, adaptive types of seasonal biological changes can be molded through evolution to fit annual environmental cycles. Studies of the formal properties of photoperiodic mechanisms have revealed that most organisms use circadian oscillators to measure day length. Two types of paradigms, designated as the external and internal coincidence models, have been proposed to account for photoperiodic time measurement by a circadian mechanism. Both models postulate that the timing of light exposure, rather than the total amount of light, is critical to the organism's perception of day length. In mammals, a circadian oscillator(s) in the suprachiasmatic nucleus of the hypothalamus receives photic stimuli via the retinohypothalamic tract. The circadian system regulates the rhythmic secretion of the pineal hormone, melatonin. Melatonin is secreted at night, and the duration of secretion varies in inverse relation to day length; thus, photoperiod information is "encoded" in the melatonin signal. The melatonin signal is presumably "decoded" in melatonin target tissues that are involved in the regulation of a variety of seasonal responses. Variations in photoperiodic response are seen not only between species but also between breeding populations within a species and between individuals within single breeding populations. Sometimes these variations appear to be the result of differences in responsiveness to melatonin; in other cases, variations in photoperiod responsiveness may depend on differences in patterns of melatonin secretion related to circadian variation. Sites of action for melatonin in mammals are not yet well characterized, but potential targets of particular interest include the pars tuberalis of the pituitary gland and the suprachiasmatic nuclei. Both these sites exhibit uptake of radiolabeled melatonin in various species, and there is some evidence for direct action of melatonin at these sites. However, it appears that there are species differences with respect to the importance and specific functions of various melatonin target sites.

Animals↗
PubMed2001

Insect photoperiodism and circadian clocks: models and mechanisms.

Photoperiodic clocks allow organisms to predict the coming season. In insects, the seasonal adaptive response mainly takes the form of diapause. The extensively studied photoperiodic clock in insects was primarily characterized by a "black-box" approach, resulting in numerous cybernetic models. This is in contrast with the circadian clock, which has been dissected pragmatically at the molecular level, particularly in Drosophila. Unfortunately, Drosophila melanogaster, the favorite model organism for circadian studies, does not demonstrate a pronounced seasonal response, and consequently molecular analysis has not progressed in this area. In the current article, the authors explore different ways in which identified molecular components of the circadian pacemaker may play a role in photoperiodism. Future progress in understanding the Drosophila circadian pacemaker, particularly as further output components are identified, may provide a direct link between the clock and photoperiodism. In addition, with improved molecular tools, it is now possible to turn to other insects that have a more dramatic photoperiodic response.

Animals↗