title: Thyroid hormone determines the start of the sensitive period of imprinting and primes later learning.
abstract: Filial imprinting in precocial birds is the process of forming a social attachment during a sensitive or critical period, restricted to the first few days after hatching. Imprinting is considered to be part of early learning to aid the survival of juveniles by securing maternal care. Here we show that the thyroid hormone 3,5,3'-triiodothyronine (T(3)) determines the start of the sensitive period. Imprinting training in chicks causes rapid inflow of T(3), converted from circulating plasma thyroxine by Dio2, type 2 iodothyronine deiodinase, in brain vascular endothelial cells. The T(3) thus initiates and extends the sensitive period to last more than 1 week via non-genomic mechanisms and primes subsequent learning. Even in non-imprinted chicks whose sensitive period has ended, exogenous T(3) enables imprinting. Our findings indicate that T(3) determines the start of the sensitive period for imprinting and has a critical role in later learning.
authors.affiliation: Faculty of Pharmaceutical Sciences, Department of Life and Health Sciences, Teikyo University, 2-11-1 Kaga, Itabashi-ku, Tokyo 173-8605, Japan.
authors.forename: Shinji
authors.initials: S
authors.lastname: Yamaguchi
authors.forename: Naoya
authors.initials: N
authors.lastname: Aoki
authors.forename: Takaaki
authors.initials: T
authors.lastname: Kitajima
authors.forename: Eiji
authors.initials: E
authors.lastname: Iikubo
authors.forename: Sachiko
authors.initials: S
authors.lastname: Katagiri
authors.forename: Toshiya
authors.initials: T
authors.lastname: Matsushima
authors.forename: Koichi J
authors.initials: KJ
authors.lastname: Homma
mesh_terms: D000818:Animals; D002645:Chickens; D007173:Imprinting, Psychological / Q000502:physiology*; D007453:Iodide Peroxidase / Q000378:metabolism; D007858:Learning / Q000502:physiology*; D013963:Thyroid Hormones / Q000097:blood* / Q000378:metabolism; D013974:Thyroxine / Q000097:blood / Q000378:metabolism; D014284:Triiodothyronine / Q000097:blood / Q000378:metabolism; D000097564:Iodothyronine Deiodinase Type II
chemical_list: D007453:Iodide Peroxidase; D013963:Thyroid Hormones; D013974:Thyroxine; D014284:Triiodothyronine; D000097564:Iodothyronine Deiodinase Type II