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

描述（由申请人提供）：本研究的总体目标是评估杀虫剂西维因如何改变甲状腺激素的作用，从而影响关键的发育过程。我们将使用非哺乳动物的两栖动物模型，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）两栖动物对环境污染物敏感，因为卵、鳃和皮肤是可渗透的; 3）以前对两栖动物的研究表明，暴露于杀虫剂西维因会导致早熟变态，这表明甲状腺激素的作用受到暴露的影响; 4）甲状腺激素发挥其细胞效应的机制在脊椎动物（包括人类）中高度保守。拟议的研究将评估中心假设，即暴露于亚致死浓度的杀虫剂会诱导甲状腺激素作用，这会对个体无尾两栖类的生长、发育、行为和生存产生负面影响。为了验证我们的假设，我们将利用分子生物学技术、实验室和野外研究，对从孵化到变态和进入陆地环境的绿色蛙进行以下具体目标的检验：（1）评估暴露于杀虫剂西维因对甲状腺激素作用、变态时间、变态时的大小和变态前的存活率的影响;（2）研究在不同发育阶段暴露于西维因的时间如何影响甲状腺激素的作用和早熟变态的发生率;（3）确定在变化的幼虫密度的条件下，西维因暴露对甲状腺激素的作用和变态的影响程度，这是一种应激的自然条件;（4）通过评估变态蛙的陆地表现，确定幼虫暴露于西维因对以后生命阶段的影响。所有动物在经历细胞增殖或现有身体计划的一般重塑（例如，胚胎发育、变态、婴儿期、儿童期发育、性发育）。证明环境相关浓度的西维因可以在实验室和现场诱导甲状腺激素作用，这将提供强有力的证据表明，在自然条件下，类似的生化效应可能发生在人类身上;这项研究还将表明自然环境压力如何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与理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的环境污染物的生物学效应相关的NIH目标。 项目叙述：证明环境相关浓度的西维因可以诱导甲状腺激素的作用，并且在两栖动物模型中发育的时间会影响这种反应，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，这些变化可以影响大脑发育，身体发育，行为以及未来的生长和生存。这项研究可能表明，人类在快速生长和发育期间，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最不利影响。我们提出的研究使用两栖动物模型，可以帮助解释环境污染在各种现象中的作用，如甲状腺疾病，行为障碍和人类早熟，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.