Central regulation of the hypothalamic-pituitary-thyroid (HPT) axis
The hypothalamic-pituitary-thyroid (HPT) axis primarily functions to maintain normal, circulating levels of thyroid hormones that are essential for the biologic function of all tissues including brain development, regulation of cardiovascular, bone and liver function, food intake and energy expenditure among many others.
The main central regulators of the HPT axis are the hypophysiotropic thyrotropin-releasing hormone (TRH) synthesizing neurons residing in the hypothalamic paraventricular nucleus (PVN). These neurons integrate a wide variety of humoral and neuronal signals and regulate TSH synthesis and release of the anterior pituitary and this way regulate the thyroid hormone synthesis of the thyroid gland. One of the main mechanisms that regulate the hypophysiotropic TRH neurons is the thyroid hormone negative feedback regulation. In addition to the hypophysiotropic TRH neurons, a second hypothalamic cell group, the tanycytes also play crucial role in this regulatory mechanism. These cells take up the inactive form of thyroid hormones, the T4, from the blood, convert it to the active T3 and release it to the hypothalamus. This way the tanycytes can modulate the feedback regulation of TRH neurons.
Using transgenic animals, morphological and electrophysiological tools, our laboratory explores, how the hypophysiotropic TRH neurons are integrated into neuronal networks and how the interaction of the hypophysiotropic TRH neurons and the tanycytes regulates the HPT axis. We also study, the development of the negative feedback regulation and how the HPT axis is regulated in non-thyroidal illness syndrome.