Thyroid hormones are essential for development of the central nervous system and deficits in these hormones during development affects such cognitive functions as learning and memory (Ambrogini et al., 2005, Chan and Kilby, 2000). Thyroid hormones exert their physiological role mainly through binding to specific nuclear receptors including the predominant isoforms of thyroid hormone receptors TRa1, TRa2, TR 1 and TR 2. TRa1, TR 1 and TR 2 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 (Constantinou et al., 2005). Anti-Thyroid Hormone Receptor, -Isotype Western blot of hippocampal lysate showing specific immunolabeling of the ~58k TR- protein.