Influence of test duration on the sensitivity of the two-bottle choice test

The long-term two-bottle choice test is commonly used as a simple screen to examine the acceptance of taste solutions by rodents. As part of an investigation of factors influencing the sensitivity of the two-bottle choice test, we determined the extent to which test duration influenced test sensitivity. C57BL6/J and 129X1/SvJ mice received four series of eight two-bottle tests, with each test lasting 1, 2, 4 or 6 days. Each series involved sequential tests with water, 2 mM saccharin, 5 and 50 mM citric acid, 30 and 300 micro M quinine hydrochloride, 75 mM NaCl and 10% ethanol. There were significant differences between the strains in intake of saccharin, 5 and 50 mM citric acid, NaCl and ethanol in 4 and 6 day tests, but only saccharin and ethanol in 2 day tests, and 5 mM citric acid and ethanol in 1 day tests. To compare the sensitivity of the tests, we developed an analytical approach based on the comparison of deviations of individual 129X1/SvJ mice from the C57BL6/J strain mean. Our results suggest that to discriminate between strains or treatments when using 'standard' laboratory conditions and methods, 1 day tests are generally inadequate and 2 day tests are useful only if large effects are anticipated. Tests lasting 4 or 6 days are more sensitive, but conducting 6 day tests provides little additional benefit and sometimes is detrimental relative to conducting 4 day tests.     

Comparison of the saline infusion test and the fludrocortisone suppression test for the diagnosis of primary aldosteronism

For the diagnosis of primary aldosteronism (PA), confirmatory testing is mandatory and different function tests can be employed. There are, however, sparse data comparing the fludrocortisone suppression test (FST) and the saline infusion test (SIT). Patients with PA (n=90) or essential hypertension (n=65) were studied. They underwent one or the other test or both of them. Using the DPC Siemens aldosterone radioimmunoassay, we found that the SIT led to a stronger suppression of aldosterone than the FST. Post-test aldosterone-to-renin ratios (ARRs) and the percentage of suppression of aldosterone serum concentrations performed worse. The same results were observed in patients who underwent both FST and SIT. Some patients had divergent results in both tests. For the SIT, a lower cutoff value should be used than for the FST for the adequate identification of patients with unilateral PA. Long-term prospective studies are needed to address the question at what cutoff values patients benefit from subtype differentiation of PA. We discuss here possible explanations for divergent results obtained with both tests.     

The HKA test revisited: a maximum-likelihood-ratio test of the standard neutral model

We present a maximum-likelihood-ratio test of the standard neutral model, using multilocus data on polymorphism within species and divergence between species. The model is based on the Hudson-Kreitman-Aguade (HKA) test, but allows for an explicit test of selection at individual loci in a multilocus framework. We use coalescent simulations to show that the likelihood-ratio test statistic is conservative, particularly when the assumption of no recombination is violated. Application of the method to polymorphism data from 18 loci from a population of Arabidopsis lyrata provides significant evidence for a balanced polymorphism at a candidate locus thought to be linked to the centromere. The method is also applied to polymorphism data in maize, providing support for the hypothesis of directional selection on genes in the starch pathway.     

Interactions of histidine-containing test substances and extraction methods with the Ames mutagenicity test

Free histidine as well as histidine in the form of dipeptides present in food samples or biological material interacted with the Ames mutagenicity test. This event becomes especially important for test compounds that exert only weak ‘mutagenic’ effects. Histidine bound to large molecules and methyl derivatives did not affect the Ames test. For the avoidance of misinterpretations, it is therefore indispensable to determine or eliminate the interacting forms of histidine when protein-containing samples are tested in the Ames test.Extraction methods using sorbants and solvents that contain contaminants or can induce chemical reactions with biological test substances should be well controlled or avoided. Solvents such as alcohols, esters and aliphatic hydrocarbons that would minimally react with such test material should therefore be used for extraction.     

Statistical analysis of the micronucleus test

Various statistical procedures are discussed to compare the incidence of micronucleated polychromatic erythrocytes between various treatment groups and a negative control. The effect of toxicity on the choice of statistical procedure is discussed. The procedure which is recommended is based on likelihood ratio tests comparing each dose group separately against the negative control. The significance level is controlled to allow for the multiple comparisons.     

Properties of the multiallelic trend test

Disease genes can be mapped on the basis of associations between genetic markers and disease status, with the case-control design having the advantage of not requiring individuals from different generations. When the marker loci have multiple alleles, there has been debate on whether the power of tests for association increases or decreases. We show here that the multiple-allele version of Armitage's trend test has increased power over the two-allele version under the requirement of equifrequent alleles, but not in general. The trend test has the advantage of remaining valid even when the sampled population is not in Hardy-Weinberg equilibrium. A departure from Hardy-Weinberg means that association tests depend on gametic and nongametic linkage disequilibrium between marker and disease loci, and we illustrate the magnitude of these effects with simulated data.