Effects of prenatal cocaine exposure on postnatal growth patterns of male Wistar rats

ADaphnia magnaFirst-Brood Chronic Test: An Alternative to the Conventional 21-Day Chronic Bioassay?

“…Therefore, despite the difficulties associated with the nonlinear regression approach, namely, the choice of the model, the use of point estimates based on the model, such as the EC , seems to be preferable. The logistic function as the solution of a differential equation stating a decrease in the relative rate of reproduction that is proportional to the number of viable offspring has the asymptotic property for low and high toxic concentrations and its graph indicates a symmetric sigmoidal course, characteristics useful in modeling reproduction or growth (Silva et al, 1995). One of the parameters used, the point of inflection, is adequate to give a direct estimation of the EC , but, instead of the rate constant, other parameters could have been used, such as the slope of the line tangent to the curve at the point of inflection, 1/4rK.…”

“…One of the parameters used, the point of inflection, is adequate to give a direct estimation of the EC , but, instead of the rate constant, other parameters could have been used, such as the slope of the line tangent to the curve at the point of inflection, 1/4rK. Other models, such as the Gompertz model (Silva et al, 1995), could be used, but then other parameters would be estimated, since its point of inflection does not lead directly to the estimation of the concentration that would cause of 50% reduction in reproduction, but to a reduction in reproduction near 37%. Nevertheless, as the objective of this work was a comparison between exposure to the toxicant until the first-brood release and 21 days of exposure, it was preferable to use the same model for the two periods, and since at the first period the logistic curve provided an adequate fit to the data, the model was kept for the subsequent period.…”

Effects of prenatal exposure to amphetamine in the medial prefrontal cortex of the rat

“…For the study of forebrain and body weight relationship of the male offspring, we used the weights of the fixed forebrain collected after perfusion at postnatal days 14, 30 and 90. 42 The data at each time point for each treatment consisted of two male pups from four different litters born to mothers of the four experimental groups, giving a total of 96 observations. The logarithmic transformation of both variables agrees with the allometric law relating growth of these two parts of the organism, 43 each of them having an exponential growth.…”

Toxicity of 4-Nonylphenol to Tubifex tubifex and Chironomus riparius in 28-Day Whole-Sediment Tests

“…The observed symmetric sigmoidal "t of the graph (Fig. 3) is considered proper in modeling reproduction or growth (Silva et al, 1995).…”

“…The number of the eggs and the young worms, which are continuous data, were "tted by a sigmoid curve. The logistic model was obtained by a more general model largely used in pharmacology to detect dose}response e!ects (Neter et al, 1985;Silva et al, 1995) and more recently also used in ecotoxicology (OECD, 1995;Field et al, 1999;Guilhermino et al, 1999). …”