Altered magnetic resonance images of brain and social behaviors of hatchling, and expression of thyroid hormone receptor βmRNA in cerebellum of embryos after Methimazole administration.
OBJECTIVE
The effects of low thyroid hormone level during embryogenesis on MRI of the brain and social behaviors of hatchlings were examined using "fertilized hen's egg-embryo-chick" system.


RESULTS
Control and hatchlings treated with methimazole (20 μmol/egg), which hatched 3 days later than controls were examined. The results are as follows: 1. The MRI examination of the midsagittal section of the brain on hatch day showed that the sizes, by T1- and ADC values by diffusion-weighted images, of the optic lobe and cerebellum of the MMI-hatchlings were significantly bigger than those of the controls. 2. The social behaviors on post-hatch day 3 were based on the following tests: (a) Aggregation test: The speed of four chicks, individually isolated by cardboard barriers in a box, to make a group upon the removal of barriers. (b) Belongingness tests: The speed of a chick isolated at a corner to join the group of three chicks placed at the opposite corner. (c) Vocalization test: The number of decibel produced by a chick isolated at a corner using a sound meter. These tests demonstrated that MMI-hatchlings took longer times and had weaker vocalization than the controls, significantly. 3. Upregulation of THRβ mRNA after MMI treatment suggested that THR was necessary for cerebellum development.


CONCLUSIONS
The MMI exposure during the last week of embryogenesis possibly delayed the myelination of certain brain regions and impaired the social behaviors of hatchlings. The chick embryos can be easily induced with hypothyroidism without maternal influences, and the hatchling's behaviors were analyzed using a video camera. The present method will be useful for assessing the effects of unfavorable influences during embryogenesis on social behaviors in later life.
Department of Obstetrics and Gynecology, School of Medicine, Iwate Medical University, Morioka, Iwate, 020-0023, Japan.
Gen
G
Haba
Hidekazu
H
Nishigori
Makoto
M
Sasaki
Koujiro
K
Tohyama
Kohsuke
K
Kudo
Yutaka
Y
Matsumura
Toru
T
Sugiyama
Keisuke
K
Kagami
Yu
Y
Tezuka
Atsushi
A
Sanbe
Hideo
H
Nishigori
D000818:Animals; D000831:Animals, Newborn; D013956:Antithyroid Agents / Q000494:pharmacology*; D001010:Anxiety, Separation / Q000523:psychology; D001921:Brain / Q000033:anatomy & histology / Q000187:drug effects* / Q000196:embryology; D001923:Brain Chemistry / Q000187:drug effects / Q000502:physiology*; D002531:Cerebellum / Q000033:anatomy & histology / Q000187:drug effects* / Q000196:embryology; D002642:Chick Embryo; D002645:Chickens; D038524:Diffusion Magnetic Resonance Imaging; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging; D008713:Methimazole / Q000494:pharmacology*; D004856:Postural Balance / Q000187:drug effects; D012333:RNA, Messenger / Q000096:biosynthesis* / Q000235:genetics; D012919:Social Behavior; D037042:Thyroid Hormone Receptors beta / Q000096:biosynthesis* / Q000235:genetics; D014284:Triiodothyronine / Q000502:physiology; D015854:Up-Regulation / Q000187:drug effects; D014828:Vocalization, Animal
D013956:Antithyroid Agents; D012333:RNA, Messenger; D037042:Thyroid Hormone Receptors beta; D014284:Triiodothyronine; D008713:Methimazole