Changing measurement instrument at follow-up a potential source of error

The purpose of this investigation was to determine whether headache activity information collected over the phone can be directly compared with headache activity information collected by systematic self-observation without jeopardizing internal validity because of calibration differences between the two measurement methods. A number of headache studies have relied on phone information for long-term follow-up data, while using systematic self-observation to collect all other data. Twenty-six headache sufferers participating in a tension headache study reported their headache activity over the phone and subsequently charted their headaches. Correlations were computed between the two measures. Results indicated that differences exist in the calibration of the two measurement methods. This seriously limits the conclusions of studies that used phone information to obtain follow-up data. Other recommendations concerning follow-up methodologies are discussed.     

Sucrose acceptance threshold: a way to measure sugar perception in ants

Variation in the perception of sweet taste is a well-known phenomenon in the animal kingdom. Well-established protocols for measuring sucrose responsiveness in non-social insects and honeybees have made it possible to understand many aspects of their biology and behaviour. Ants are also advanced social insects that present a plethora of life histories with diverse strategies and behaviours; however, a universal paradigm possible to measure this response in different ant species has not yet been developed. Here, we present a protocol for measuring the sucrose acceptance threshold (SAT) under controlled conditions in harnessed ants with different feeding habits. By testing the response to antennal and palp sucrose stimulation and using the occurrence of licking as the response, we developed a non-ambiguous evaluation that allowed easy detection of threshold changes. The results showed that the response to both antennal and palp stimulation varied widely among species. Some species licked in response to antennal stimulation while others did so in response to palp stimulation. Using the appropriate kind of stimulation, we tested the SAT protocol in ants of different genera and ants of the same species with different levels of sugar reserve. The differences detected in both cases imply that the protocol is appropriate for measuring and detecting variations in sugar perception in ants.     

Photooxidation of NADH by 2,3-butanedione: a potential source of error in studies on active site arginyl residues.

Incubation of NADH or NADPH with 2,3-butanedione in aqueous solution results in photooxidation of the reduced pyridine nucleotides under conditions of ordinary laboratory lighting. Maximum rates of photooxidation are obtained at pH 7 and with light at a wavelength of 410 nm. This reaction could lead to artifactual results in experiments on the role of arginyl groups in enzymes in which a reduced pyridine nucleotide is used to protect the active site residues from modification by 2,3-butanedione.     

Lipogranulomatous lymphadenopathy as a potential source of error in fine needle aspiration cytology. A case report

BACKGROUND: Lipogranulomatosis refers to the presence, in lymph nodes and spleen, of lipid material arising from endogenous sources, such as tumors, hematomas, cholesterol deposits, fat embolism and fat necrosis. The histologic image is similar to that seen in lymph nodes after lymphography, with vacuolized histiocytes; round, empty spaces; and numerous multinucleated giant cells (MGC). CASE: A 27-year-old woman was referred to our department for fine needle aspiration of bilateral inguinal lymph nodes. One year before, a giant cell tumor of the sacrum was surgically excised at another medical center. The aspirated material showed a normal lymphoid cell background in addition to several MGC and ill-defined cellular groups of mononuclear, histiocytelike cells admixed with mature lymphocytes. After the cytologic report was issued both nodes were surgically excised. The most remarkable histologic finding was the presence of sinus histiocytosis and multifocal subcapsular and sinusoidal lipogranulomas with numerous MGC. CONCLUSION: Lipogranulomatous lymphadenopathy is a rare pathologic condition and may be responsible for smears with numerous MGC. This entity should be considered when evaluating lymph node aspirates from patients with neoplasia, particularly that with a giant cell component.     

Dye shift: a neglected source of genotyping error in molecular ecology

Molecular ecologists must be vigilant in detecting and accounting for genotyping error, yet potential errors stemming from dye-induced mobility shift (dye shift) may be frequently neglected and largely unknown to researchers who employ 3-primer systems with automated genotyping. When left uncorrected, dye shift can lead to mis-scoring alleles and even to falsely calling new alleles if different dyes are used to genotype the same locus in subsequent reactions. When we used four different fluorophore labels from a standard dye set to genotype the same set of loci, differences in the resulting size estimates for a single allele ranged from 2.07 bp to 3.68 bp. The strongest effects were associated with the fluorophore PET, and relative degree of dye shift was inversely related to locus size. We found little evidence in the literature that dye shift is regularly accounted for in 3-primer studies, despite knowledge of this phenomenon existing for over a decade. However, we did find some references to erroneous standard correction factors for the same set of dyes that we tested. We thus reiterate the need for strict quality control when attempting to reduce possible sources of genotyping error, and in cases where different dyes are applied to a single locus, perhaps mistakenly, we strongly discourage researchers from assuming generic correction patterns.     

Humidity as a source of measurement error in osteometrics

A simple experiment was conducted to test the hypothesis that variation in humidity causes expansion of bone and, thereby, affects measurements of dried, preserved skulls. The experiment consisted of subjecting ten macaque skulls to increased humidity for 24 hours. Measurements of nine skull dimensions taken immediately before and after humidification revealed a statistically significant treatment effect of increased skull size with increased humidity. The length of the molar tooth row increased by about 0.1 mm (0.50%) while the greatest length of the skull increased by about 0.9 mm (0.57%). The specimens returned to their original dimensions within 1-2 days after being removed from the humidity chamber. These results confirm the impression gained by the practical experience of measuring museum specimens in different locations and environments. It appears that bony changes associated with humidity differences represent a real, though minor, source of measurement error in osteometrics.     

A potential source of error when estimating ecological production of fishes using back-calculations

Synopsis Fish production estimates determined from weights back-calculated to the time of annulus formation were found to underestimate actual production by 12 to 44%. It is suggested that production should either be estimated from weights at the time of collection or a correction factor should be employed when back-calculating weights.     

Ion channel-mediated uptake of cationic vital dyes into live cells: a potential source of error when assessing cell viability

Ionic “vital dyes” are commonly used to assess cell viability based on the idea that their permeation is contingent on a loss of membrane integrity. However, the possibility that dye entry is conducted into live cells by endogenous membrane transporters must be recognized and controlled for. Several cation-selective plasma membrane-localized ion channels, including the adenosine 5?-triphosphate (ATP)-gated P2X receptors, have been reported to conduct entry of the DNA-binding fluorescence dye, YO-PRO-1, into live cells. Extracellular ATP often becomes elevated as a result of release from dying cells, and so it is possible that activation of P2X channels on neighboring live cells could lead to exaggerated estimation of cytotoxicity. Here, we screened a number of fluorescent vital dyes for ion channel-mediated uptake in HEK293 cells expressing recombinant P2X2, P2X7, or TRPV1 channels. Our data shows that activation of all three channels caused substantial uptake and nuclear accumulation of YO-PRO-1, 4?,6-diamidino-2-phenylindole (DAPI), and Hoechst 33258 into transfected cells and did so well within the time period usually used for incubation of cells with vital dyes. In contrast, channel activation in the presence of propidium iodide and SYTOX Green caused no measurable uptake and accumulation during a 20-min exposure, suggesting that these dyes are not likely to exhibit measurable uptake through these particular ion channels during a conventional cell viability assay. Caution is encouraged when choosing and employing cationic dyes for the purpose of cell viability assessment, particularly when there is a likelihood of cells expressing ion channels permeable to large ions.     

Cysteine: a potential source of error in amino acid analysis of mercaptoethane sulfonic or hydrochloric acid hydrolysates of proteins and peptides

Hydrolysis of proteins and peptides with mercaptoethane sulfonic acid is liable to produce overestimation of the proline content owing to the production of ninhydrin-positive material (probably cysteine) which coelutes with proline on many ion-exchange analytical systems. A similar error occurs with HCl hydrolysis (especially in the presence of mercaptoethanol or thioglycollic acid) if care is not taken to oxidize cysteine during reconstitution of the hydrolysate before amino acid analysis.     

Kluyveromyces marxianus: a potential source of diacetyl reductase

Kluyveromyces marxianus had a higher specific activity of diacetyl reductase (EC 1.1.1.5) than all other organisms previously reported. The enzyme was NADH-dependent and irreversibly catalysed the conversion of diacetyl to acetoin with an optimum pH of 7.0. It was stable at 40°C but lost 50% of its activity at 50°C in 30 min. The K _m and V _max values for diacetyl were 1.8 mm and 0.053 mm/min, respectively.The authors are with the Department of Food Science and Technology, Comell University, Geneva, New York 14456, USA     

Variability in asthma: symptom perception, care, and outcomes

Asthma remains a global respiratory health concern. Substantial variations in asthma outcomes persist in Canada despite the dissemination of national management guidelines. Many factors and their interactions presumably contribute to variations in outcomes, including asthma prevalence, severity, symptom recognition, self-management behaviour, access to care, and management. This article reviews the physiology of symptom perception in asthma, specifically the role of dynamic lung hyperinflation (DH) on the perception of the intensity and quality of dyspnea in asthma, and the link between blunted perception and life-threatening asthma. Additionally, the magnitude and correlates of regional variation in emergency department visit rates and hospitalizations for asthma in Ontario are reviewed.     

Sound source perception in anuran amphibians

Sound source perception refers to the auditory system's ability to parse incoming sensory information into coherent representations of distinct sound sources in the environment. Such abilities are no doubt key to successful communication in many taxa, but we know little about their function in animal communication systems. For anuran amphibians (frogs and toads), social and reproductive behaviors depend on a listener's ability to hear and identify sound signals amid high levels of background noise in acoustically cluttered environments. Recent neuroethological studies are revealing how frogs parse these complex acoustic scenes to identify individual calls in noisy breeding choruses. Current evidence highlights some interesting similarities and differences in how the auditory systems of frogs and other vertebrates (most notably birds and mammals) perform auditory scene analysis.