Thyroid Hormone and Transcriptional Regulation in the Central Nervous System

Thyroid hormone (TH) is important in both the development and adult function of the central nervous system (CNS). In human development, lack of iodine or congenital abnormalities in TH production or action are known causes of mental retardation. TH action involves secretion of TH by the thyroid gland into the circulation, uptake of TH by target tissues, activation or inactivation of TH by deiodinase enzymes, binding of TH to nuclear receptors that act as ligand-regulated transcription factors, and regulation of expression of target genes. Several actions of TH in the CNS are discussed: regulation of glucose utilization, synaptic activity and oligodendrocyte differentiation; axonal and dendritic outgrowth; and differentiation of the visual and auditory systems.