Thyroid hormone homeostasis and action in the type 2 deiodinase-deficient rodent brain during development.

Considerable indirect evidence suggests that the type 2 deiodinase (D2) generates T3 from T4 for local use in specific tissues such as pituitary, brown fat, and brain, and studies with a D2-deficent mouse, the D2 knockout (D2KO) mouse, have shown this to be the case in pituitary and brown fat. The present study employs the D2KO mouse to determine the role of D2 in the developing brain. As expected, the T3 content in the neonatal D2KO brain was markedly reduced to a level comparable with that seen in the hypothyroid neonatal wild-type mouse.