title: Sex Differences in Brain Thyroid Hormone Levels during Early Post-Hatching Development in Zebra Finch (Taeniopygia guttata).
abstract: Thyroid hormones are closely linked to the hatching process in precocial birds. Previously, we showed that thyroid hormones in brain had a strong impact on filial imprinting, an early learning behavior in newly hatched chicks; brain 3,5,3'-triiodothyronine (T3) peaks around hatching and imprinting training induces additional T3 release, thus, extending the sensitive period for imprinting and enabling subsequent other learning. On the other hand, blood thyroid hormone levels have been reported to increase gradually after hatching in altricial species, but it remains unknown how the brain thyroid hormone levels change during post-hatching development of altricial birds. Here, we determined the changes in serum and brain thyroid hormone levels of a passerine songbird species, the zebra finch using radioimmunoassay. In the serum, we found a gradual increase in thyroid hormone levels during post-hatching development, as well as differences between male and female finches. In the brain, there was clear surge in the hormone levels during development in males and females coinciding with the time of fledging, but the onset of the surge of thyroxine (T4) in males preceded that of females, whereas the onset of the surge of T3 in males succeeded that of females. These findings provide a basis for understanding the functions of thyroid hormones during early development and learning in altricial birds.
authors.affiliation: Department of Life and Health Sciences, Faculty of Pharmaceutical Sciences, Teikyo University, Kaga, Itabashi-ku, Tokyo, Japan.
authors.forename: Shinji
authors.initials: S
authors.lastname: Yamaguchi
authors.affiliation: Department of Biology, Faculty of Science, Hokkaido University, Hokkaido, Japan.
authors.forename: Shin
authors.initials: S
authors.lastname: Hayase
authors.affiliation: Department of Life and Health Sciences, Faculty of Pharmaceutical Sciences, Teikyo University, Kaga, Itabashi-ku, Tokyo, Japan.
authors.forename: Naoya
authors.initials: N
authors.lastname: Aoki
authors.affiliation: Department of Life and Health Sciences, Faculty of Pharmaceutical Sciences, Teikyo University, Kaga, Itabashi-ku, Tokyo, Japan.
authors.forename: Akihiko
authors.initials: A
authors.lastname: Takehara
authors.affiliation: Department of Biology, Faculty of Science, Hokkaido University, Hokkaido, Japan.
authors.forename: Jun
authors.initials: J
authors.lastname: Ishigohoka
authors.affiliation: Department of Biology, Faculty of Science, Hokkaido University, Hokkaido, Japan.
authors.forename: Toshiya
authors.initials: T
authors.lastname: Matsushima
authors.affiliation: Department of Biology, Faculty of Science, Hokkaido University, Hokkaido, Japan.
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Wada
authors.affiliation: Department of Life and Health Sciences, Faculty of Pharmaceutical Sciences, Teikyo University, Kaga, Itabashi-ku, Tokyo, Japan.
authors.forename: Koichi J
authors.initials: KJ
authors.lastname: Homma
mesh_terms: D000818:Animals; D001921:Brain / Q000254:growth & development* / Q000378:metabolism*; D005260:Female; D046369:Finches / Q000502:physiology*; D015870:Gene Expression; D007453:Iodide Peroxidase / Q000235:genetics / Q000378:metabolism; D008297:Male; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D011988:Receptors, Thyroid Hormone / Q000378:metabolism; D012727:Sex Characteristics; D013963:Thyroid Hormones / Q000097:blood / Q000378:metabolism*
chemical_list: D012333:RNA, Messenger; D011988:Receptors, Thyroid Hormone; D013963:Thyroid Hormones; D007453:Iodide Peroxidase