signaling pathway pertinent to the brain and nervous system tyrosine-based hormone signaling pathway thyroid hormone signaling pathway PW:0000501 TH signaling pathway Thyroid hormone (TH) signaling pathway plays important roles in glucose and lipid metabolism. The TH receptors are nuclear receptors that once activated act as transcription factors. Low levels of TH stimulate the release of thyrotropin-releasing hormone (TRH) from the hypothalamus, in turn stimulating the secretion of thyroid-stimulating hormone (TSH) from the pituitary whose signaling then triggers TH production. TRH, TSH and TH signaling pathways are part of the hypothalamic-pituitary-thyroid (HPT) axis for which TH itself provides a negative regulatory loop. pathway