Hormone-receptor interactions in brain: Uptake and binding of thyroid hormone

(1) The uptake and localization of thyroid hormones in the cerebral cortex and in its subcellular fractions were determined in vivo and in vitro, and specific hormone receptors were sought in nuclei and mitochondria. (2) Our observations indicate that whereas uptake and localization of thyroid hormones is higher in mitochondria and synaptosomal fractions than in nuclear fractions, specific binding is found in the nuclei only. (3) The apparent number of binding sites is high in cerebral cortex and in pituitary compared with liver and hypothalamus, an observation which can be correlated with the action of thyroid hormones on cerebral cortical function and regulation of pituitary-thyroid feedback.