ABSTRACT
Thyroid hormone (TH) is essential for normal brain development (1-4). Exposure to severe
TH insufficiency during fetal and/or neonatal development in humans leads to a condition
known as cretinism, characterized in part by severe mental retardation (5). Likewise,
exposure to severe TH insufficiency during fetal and/or neonatal development in
experimental animals leads to severe behavioral impairment indicative of neurodevelop-
mental deficits (6). Considering these observations, it is reasonable to predict that any
environmental chemical affecting TH action during brain development may produce
adverse effects on cognitive development (7). However, there are several reasons that
testing this prediction is not currently a simple matter. Therefore, the goal of this chapter is
to provide an analysis of the challenges to investigators engaged in basic research focused
on providing information to be used in risk assessment. The point of departure for this
chapter is the recommendation by the U.S. EPA Endocrine Disruptor Screening and Testing
Advisory Committee (EDSTAC) for assays to be used to screen for thyroid toxicants.
