Finding the Way into the Brain without MCT8

How does thyroid hormone (TH) find its way into the brain? Although it has been known for a long time thatTHis crucial for normal brain development, the exact molecular mechanisms involved in TH transport in the brain have remained elusive until recently. Early studies showed selective and saturable accumulation of TH in particular brain regions, suggesting that active transport processes are required forTHentry across the blood-brain barrier (BBB) and into brain cells (1). The discovery that TH transporter proteins located in the plasma membrane are required for cellular entry of the hormone has advanced our understanding of TH physiology. Thus, TH transporters mediate transport not only across the BBB but also into each individual cell of the brain.