Perinatal problems in thyroid gland physiology are common but complicated and present a diagnostic dilemma for the primary clinician. In December 1990, an international group of basic and clinical investigators gathered in Longboat Key, Florida to address these issues. The participants included internists, obstetricians, pedia- tricians, neurologists, pathologists and basic scientists in cellular metabolism, endocrine physiology, and molecular biology. The presentations contained within this book bring together their most current and vital research related to the field of perinatal thyroidology. This book is based on the dynamic and fruitful exchange of the participants at the symposium. We are indebted to these individuals whose valuable insights and efforts are contained within this text. Barry B. Bercu Dorothy I. Shulman vii CONTENTS Session I Mechanism of Thyroid Hormone Action 1 Leslie J. DeGroot Thyroid System Ontogeny in the Sheep: A Model for Precocial Mammalian Species * . . * * 11 Delbert A. Fisher Pathologic Studies of Fetal Thyroid 27 Development * * * * * * * Douglas R. Shanklin Thyroid Hormone Control of Brain and Motor Development: Molecular, Neuroanatomical, 47 and Behavioral Studies * * * * * * * S. A. Stein, P. M. Adams, D. R. Shanklin, G. A. Mihailoff, and M. B. Palnitkar The Thyroidectomized Pregnant Rat: An Animal Model to Study Fetal Effects of Maternal Hypothyroidism 107 Susan P. Porterfield and Chester E.