Thyroid hormones are essential for development of the central nervous system. Deficits in these hormones during development affect cognitive functions as learning and memory. Thyroid hormones exert their physiological role mainly through binding to specific nuclear receptors including the predominant isoforms of thyroid hormone receptors TRa1, TRa2, TRb1 and TRb2. TRa1, TRb1 and TRb2 bind T3 with high affinity and also bind to thyroid hormone response elements (TREs) on chromatin to regulate the transcriptional processes in several target tissues, including adult rat brain.