GLUCOCORTICOIDS STIMULATE THYROTROPIN-RELEASING-HORMONE GENE-EXPRESSION IN CULTURED HYPOTHALAMIC NEURONS

Although there is much evidence indicating that glucocorticoids (GC) i nhibit the hypothalamic-pituitary-thyroid axis in both rat and man in vivo, there have been no previous studies on the direct effect of GC o n hypothalamic TRH neurons in vitro. In this laboratory we developed f etal rat (day 17) diencephalic neuronal cultures in the presence of 5' -bromo-2-deoxyuridine, a cell-differentiating agent that stimulates TR H gene expression. In 12 separate experiments, dexamethasone (Dex) ind uced a 2.2-fold increase in TRH content us. the control value (P < 0.0 1). Dex (10(-8) M) enhanced TRH messenger RNA (mRNA) 1.6-fold (n = 75 wells; P < 0.01) by nonisotopic in situ hybridization. On Northern blo t analysis using a P-32-labeled complementary RNA probe, TRK mRNA was enhanced 3-fold (n = 4; P < 0.01). Nuclear run-on analysis revealed th at Dex enhanced transcription 7.7-fold (n = 3;P < 0.01). We conclude t hat 1) Dex stimulates the expression of TRH peptide and TRH mRNA in cu ltured hypothalamic neurons; 2) the increase in TRH mRNA results (at l east in part) from enhanced transcription; and 3) the reported in vivo depression of TRH in the paraventricular nucleus after GC stimulation suggests that this effect must be mediated indirectly on the TRH neur on.