Modeling Effective Dosages in Hormetic Dose-Response Studies

BACKGROUND: Two hormetic modifications of a monotonically decreasing log-logistic dose-response function are most often used to model stimulatory effects of low dosages of a toxicant in plant biology. As just one of these empirical models is yet properly parameterized to allow inference about quantities of interest, this study contributes the parameterized functions for the second hormetic model and compares the estimates of effective dosages between both models based on 23 hormetic data sets. Based on this, the impact on effective dosage estimations was evaluated, especially in case of a substantially inferior fit by one of the two models. METHODOLOGY/PRINCIPAL FINDINGS: The data sets evaluated described the hormetic responses of four different test plant species exposed to 15 different chemical stressors in two different experimental dose-response test designs. Out of the 23 data sets, one could not be described by any of the two models, 14 could be better described by one of the two models, and eight could be equally described by both models. In cases of misspecification by any of the two models, the differences between effective dosages estimates (0-1768%) greatly exceeded the differences observed when both models provided a satisfactory fit (0-26%). This suggests that the conclusions drawn depending on the model used may diverge considerably when using an improper hormetic model especially regarding effective dosages quantifying hormesis. CONCLUSIONS/SIGNIFICANCE: The study showed that hormetic dose responses can take on many shapes and that this diversity can not be captured by a single model without risking considerable misinterpretation. However, the two empirical models considered in this paper together provide a powerful means to model, prove, and now also to quantify a wide range of hormetic responses by reparameterization. Despite this, they should not be applied uncritically, but after statistical and graphical assessment of their adequacy

Método para avaliação da conduta visual de lactentes A method to evaluate visual ability in infants

O objetivo deste estudo é apresentar um método para avaliação de funções visuais em lactentes no primeiro trimestre de vida. Utilizou-se o Roteiro de Avaliação da Conduta Visual em Lactentes, modificado de Gagliardo (1997). O material foi aro suspenso por cordão. Realizou-se estudo piloto com 33 lactentes, segundo os critérios de inclusão: neonatos assintomáticos, sem necessidade de cuidados especiais nas primeiras 48 horas; idade cronológica variando entre 1 e 3 meses; avaliação mensal sem nenhuma falta; procedência da região de Campinas/SP. No 1º mês destacaram-se as provas: fixação visual-93,9%; contato de olho-90,9%; seguimento visual horizontal-72,7% e exploração visual do ambiente-97,0%. No 3º mês: exploração visual da mão-42,4% e aumento da movimentação de braços-36,4%. Este Roteiro permitiu observar a função visual segundo a idade cronológica; desvio dessa função possibilitará pronto encaminhamento a serviços médicos para diagnóstico.<br>The purpose of this study is to introduce a method to evaluate visual functions in infants in the first three months of life. An adaptation of the Guide for the Assessment of Visual Ability in Infants (Gagliardo, 1997) was used. The instrument was a ring with string. It was implemented a pilot study with 33 infants, selected according to the following criteria: neonates well enough to go home within two days of birth; 1 to 3 months of chronological age; monthly evaluation with no absence; subjects living in Campinas/SP metropolitan area. In the first month we observed: visual fixation (93,9%); eye contact (90,9%); horizontal tracking (72,7%); inspects surroundings (97,0%). In the third month, we observed: inspects own hands (42,4%) and increased movements of arms (36,4%). This method allowed the evaluation of visual functions in infants, according to the chronological age. Alterations in this function will facilitate immediate referral to medical services for diagnoses

Allelopathic and autotoxicity effects of barley (Hordeum vulgare L. ssp. vulgare) root exudates

The allelopathic activity of barley (Hordeum vulgare L. ssp. vulgare) root exudates was studied by comparing their effects on seedling establishment in barley itself and in two weed species, Bromus diandrus Roth. and Lolium rigidum Gaudin, using an original laboratory protocol, named ‘seed-after-seed’. In this protocol, the donor and the receiver species of watersoluble allelochemicals are grown one after the other in the same dishes, in conditions reducing resource competition between both species. Growth of all receptive species (weeds and barley) was inhibited in a dose-dependent manner, when using increasing barley seed densities (0, 8, 19 and 25 seeds per Petri dish). In our conditions, the barley varieties and landraces exhibited different allelopathic activities against weeds or barley. The allelopathic potential of the barley root exudates was also dependent on the receiver species. Indeed, the released allelochemicals proved to be more toxic against the weed plants than on barley itself. Furthermore, the toxicity of the allelochemicals increased after their release by roots, between day 0 and day 6. These allelochemicals might contribute to the plant community dynamics and their usefulness as bio-herbicides deserves further consideration