Molecular Basis of Thyroid Hormone-Dependent Brain Development*

I. Introduction II. Developmental Schedules A. Species specificity B. Developmental studies in the rat III. Thyroid Hormone Action A. Sources of T4 and T3 B. The role of maternal thyroid hormone in fetal brain development: direct or indirect? C. Intracerebral transport IV. Molecular Actions of Thyroid Hormone in the Developing Brain A. Nuclear receptors for thyroid hormone in brain B. Thyroid hormone receptor isoforms and their tissue distribution C. Interactions of ligand, receptor, and DNA D. Ontogeny of thyroid hormone receptor isoforms in brain E. Search for T3-responsive genes in the neonatal rat brain F. Regulation of gene expression by T3 through indirect molecular pathways? G. Extranuclear actions of T4? V. Theories and Speculations VI. Conclusions