Establishment of functional "hypothalms-thymus" axis at early stage of fetal life

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This study was aimed to examine when functional "crosstalk" between hypothalamus and thymus would be established during pregnancy. The hypothalamus and thymus from 13-to 21-day-old rat fetuses of Wistar strain were dissected out and then offered to (1) EIA assay of estrogen receptor (ER) and serum thymic factor (FTS) , and (2) immunohistochemical staining of ER,FTS and luteinizing hormone releasing hormone (LHRH) .ER and FTS were detectable at the 13th day of gestation, and their concentrations gradually increased until the end of gestation. LHRH was detectable in the thymus at the 13th day, wheras it appeared much later in the hypothalamus at the 16th day. ER-, FTS- and LHRH-positive cells were localized in the epithelial cells (TEC) in the thymic medullary region and the bipolar neurons in the medial preoptic area (MPOA) of the hypothalamus. In adition, all ER-, FTS-, and LHRH-positive cells in the respective tissue areas were identical with each other.It is clear from the above results that estrogen in the fetal blood circulation modulate through its receptor TEC and MPOA-neurons to release FTS and LHRH,suggesting that the functional "hypothalamus-thymus" axis is established at the early stage of the fetal life.