GLUCOCORTICOIDS INHIBIT STRESS-INDUCED PHOSPHORYLATION OF CREB IN CORTICOTROPIN-RELEASING HORMONE NEURONS OF THE HYPOTHALAMIC PARAVENTRICULAR NUCLEUS

The corticotropin-releasing hormone (CRH) gene contains a perfect pali ndromic motif in its promoter region that allows binding of the cyclic adenosine monophosphate response element binding protein, CREB. Since previous studies suggest that the CRH gene can be activated by cyclic adenosine monophosphate, we determined whether stress and feedback in hibition by glucocorticoids in CRH-producing neurons in the hypothalam ic paraventricular nucleus could be mediated by changes in the phospho rylation of CREB. Antisera to CREB and phospho-CREB Ser(133) (PCREB), the active phosphorylated form of CREB, were used for immunohistochemi cal studies on rat brain. In nonstressed animals CREB immunostaining w as confined to the nucleus of cells ubiquitously throughout the hypoth alamus, while PCREB immunostaining was discretely localized in magnoce llular neurons and only a few cells in the medial parvocellular subdiv ision of the paraventricular nucleus. Ether and handling stress marked ly increased the number of PCREB-labeled neurons in the parvocellular subdivision. Double immunolabeling with CRH antiserum revealed that th e majority of hypophysiotropic CRH neurons in stressed animals express ed PCREB. Following systemic administration of dexamethasone (100 mu g /day) for 2.5 days, PCREB immunostaining was completely abolished in p arvocellular CRH-producing neurons after ether or handling stress. Dex amethasone had no apparent effect on CREB immunostaining, These result s demonstrate that glucocorticoids suppress CREB phosphorylation in hy pophysiotropic CRH neurons and suggest that prevention of CREB phospho rylation is a possible mechanism for feedback inhibition of CRH biosyn thesis by glucocorticoids.