Administration of thyroid hormone increases reelin and brain-derived neurotrophic factor expression in rat...

Thyroid hormones play important roles in the maturation and function of the central nervous system. However, the underlying mechanism behind thyroid hormone-regulated gene expression in the adult brain is not well understood. Two genes critical for neuronal plasticity and implicated in psychiatric disorders, reelin and brain-derived neurotrophic factor (BDNF), were investigated in the present study. Triiodothyronine (T3), the active form of thyroid hormone was administered to young adult rats in two different manners: systemic injection or local brain infusion. Real time RT-PCR results revealed that T3 administration lead to a significant increase in reelin, total BDNF and exon-specific BDNF mRNA expression in the hippocampus. Furthermore, the association of transcriptional coactivators (including steroid receptor coactivator-1 (SRC-1), cAMP response element binding protein-binding protein (CBP), and thyroid hormone receptor associated protein 220 (TRAP 220)) and RNA polymerase II (RNA Pol II), with reelin and BDNF genes in the rat hippocampus displayed a distinct process following thyroid hormone administration. These findings suggest that association of transcriptional coactivators and RNA Pol II with gene promoters may be a possible mechanism explaining T3-induced reelin and BDNF expression in the hippocampus of young adult rats.