Use of an Amphibian as an Alternative Model to Evaluate Effects of Contaminants o

描述(申请人提供)：这项研究的首要目标是评估杀虫剂西维因如何改变甲状腺激素的作用，进而影响关键的发育过程。我们将使用非哺乳动物两栖动物模型，因为1)两栖动物经历变态，这是在甲状腺激素的直接控制下；2)两栖动物由于卵、鳃和皮肤具有渗透性，对环境污染物很敏感；3)以前对两栖动物的研究表明，暴露在杀虫剂西维因下可导致早熟变态，这表明甲状腺激素的作用受到暴露的影响；4)甲状腺激素产生细胞效应的机制在脊椎动物中高度保守，包括人类。这项拟议的研究将评估一个中心假设，即暴露于亚致死浓度的杀虫剂会诱导甲状腺激素作用，从而对个体无尾两栖动物的生长、发育、行为和生存产生负面影响。为了评估我们的假设，我们将使用分子技术以及实验室和野外研究来检验以下特定目标：(1)评估杀虫剂西维因对甲状腺激素作用、变态时间、变态大小和变态存活率的影响；(2)研究在不同发育阶段暴露于西维因对甲状腺激素作用和早熟变态发生率的影响；(3)确定在幼虫密度变化的自然条件下，西维因暴露对甲状腺激素作用和变态的影响的程度；以及(4)通过评估变态青蛙在陆地上的表现，确定暴露于西维因的幼虫将如何影响后期生命阶段。所有动物在经历细胞增殖或对现有身体计划(例如胚胎发育、变态、婴儿期、儿童发育、性发育)进行全面改造时，可能特别容易受到污染物的影响。证明与环境有关的西维因浓度可以在实验室和田间诱导甲状腺激素活动，这将提供强有力的证据，表明在自然条件下人类也可以产生类似的生化效应；这项研究还将表明，自然环境应激源可能会进一步增加对污染物影响的敏感性。这里概述的研究将具体解决NIH的目标，这些目标与了解与人类生长和发育相关的过程以及使用非哺乳动物模型了解环境污染物的生物影响有关。 项目简介：在两栖动物模型中，证明与环境相关的西维因浓度可以诱导甲状腺激素活动，并且发育的时机会影响这种反应，这将使我们能够将污染物与不可逆转的发育变化联系起来，这些变化可能会影响大脑发育、身体发育速度、行为以及未来的生长和存活。这项研究可能表明，人类在快速生长和发育时期，特别是在胚胎发育或性成熟开始期间，可能受到污染物暴露的负面影响最大。我们建议的研究使用了一个两栖动物模型，并可以帮助解释环境污染在各种现象中所起的作用，如甲状腺疾病、行为障碍和人类的早熟，所有这些都受到或可能受到甲状腺激素的影响。

DESCRIPTION (provided by applicant): The overarching goal of this research is to evaluate how the insecticide carbaryl alters thyroid hormone action, which in turn can influence critical developmental processes. We will use a non-mammalian, amphibian model because 1) amphibians undergo metamorphosis, which is under direct control of thyroid hormones; 2) amphibians are sensitive to environmental contaminants due to permeable eggs, gills, and skin; 3) previous work with amphibians has shown that exposure to the insecticide carbaryl can lead to precocious metamorphosis, which suggests thyroid hormone action is affected by exposure; and 4) the mechanisms whereby thyroid hormones enact their cellular effects are highly conserved in vertebrates, including humans. The proposed research will evaluate the central hypothesis that exposure to a sublethal concentration of an insecticide induces thyroid hormone action, which can negatively affect growth, development, behavior, and survival of individual anurans. To evaluate our hypothesis, we will examine the following specific objectives using molecular techniques, and laboratory and field studies with green frogs, Rana clamitans, reared from hatching through metamorphosis and into the terrestrial environment: (1) Evaluate the effects of exposure to the insecticide carbaryl on thyroid hormone action, and time to metamorphosis, size at metamorphosis, and survival to metamorphosis; (2) Examine how timing of exposure to carbaryl at different stages of development affects thyroid hormone action and incidence of precocious metamorphosis; (3) Determine the magnitude of the effect of carbaryl exposure on thyroid hormone action and metamorphosis under conditions of changing larval density, a stressful natural condition; and (4) Establish how larval exposure to carbaryl will influence later life stages by evaluating terrestrial performance of metamorphosed frogs. All animals may be particularly vulnerable to contaminants when they are undergoing cell proliferation or general remodeling of existing body plans (e.g., embryonic development, metamorphosis, infancy, childhood development, sexual development). Demonstrating that environmentally relevant concentrations of carbaryl can induce thyroid hormone action in both the laboratory and the field would offer powerful evidence to suggest that similar biochemical effects could occur in humans under natural conditions; this research will also indicate how natural environmental stressors may further increase susceptibility to effects of contaminants. The research outlined here will specifically address NIH goals linked to understanding processes related to human growth and development, and the biological effects of environmental contaminants using a non- mammalian model. Project Narrative: Demonstrating environmentally relevant concentrations of carbaryl can induce thyroid hormone action and that timing of development influences this response in an amphibian model would allow us to link contaminants to irreversible developmental changes that can influence brain development, rates of physical development, behavior, and future growth and survival. This research could suggest that humans may be most negatively affected by contaminant exposure during times of rapid growth and development, especially during embryonic development or onset of sexual maturity. Our proposed research uses an amphibian model and could help explain the role environmental contamination has in diverse phenomena such as thyroid diseases, behavior disorders, and early maturation in humans, all of which are or can be influenced by thyroid hormones.