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

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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.