title: A model of the development of the brain as a construct of the thyroid system.
abstract: Thyroid hormone is essential for normal brain development. However, little is known about the molecular and cellular mechanisms that mediate thyroid hormone action on the developing brain or the developmental events selectively affected. Consequently, although a large number of environmental chemicals interfere with the thyroid system, there are few neurodevelopmental end points to recruit for toxicological studies. Therefore, my goal here is to review what is known about the relative timing of normal brain construction and thyroid system development, with special focus on the period of in utero development in humans and the comparable developmental period in laboratory rats. These data are presented as a timeline to aid in the identification of thyroid-sensitive end points in brain development and to highlight important data gaps. I discuss the known influence of certain synthetic chemicals on the thyroid system and include a brief review of the effects of developmental exposure to chemicals on thyroid system function. The relationship between the thyroid hormone and retinoic acid systems, as well as the thyroid hormone sensitivity of the developing cochlea, is also discussed.
authors.affiliation: Wildlife and Contaminants Program, World Wildlife Fund, 1250 24th Street NW, Washington, DC 20037-9736, USA. kembra.howdeshell@wwfus.org
authors.forename: Kembra L
authors.initials: KL
authors.lastname: Howdeshell
mesh_terms: D001921:Brain / Q000187:drug effects / Q000196:embryology* / Q000254:growth & development*; D003051:Cochlea / Q000187:drug effects / Q000254:growth & development; D003638:Deafness / Q000209:etiology; D005314:Embryonic and Fetal Development; D023381:Endpoint Determination; D004781:Environmental Exposure; D006801:Humans; D013961:Thyroid Gland / Q000187:drug effects / Q000196:embryology* / Q000254:growth & development*; D013963:Thyroid Hormones / Q000494:pharmacology*; D014212:Tretinoin / Q000494:pharmacology; D015262:Xenobiotics / Q000009:adverse effects*
chemical_list: D013963:Thyroid Hormones; D015262:Xenobiotics; D014212:Tretinoin