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 palindromic 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 inhibition by glucocorticoids in CRH-producing neurons in the hypothalamic paraventricular nucleus could be mediated by changes in the phosphorylation of CREB. Antisera to CREB and phospho-CREB Ser133 (PCREB), the active phosphorylated form of CREB, were used for immunohistochemical studies on rat brain. In nonstressed animals CREB immunostaining was confined to the nucleus of cells ubiquitously throughout the hypothalamus, while PCREB immunostaining was discretely localized in magnocellular neurons and only a few cells in the medial parvocellular subdivision of the paraventricular nucleus. Ether and handling stress markedly increased the number of PCREB-labeled neurons in the parvocellular subdivision. Double immunolabeling with CRH antiserum revealed that the majority of hypophysiotropic CRH neurons in stressed animals expressed PCREB. Following systemic administration of dexamethasone (100 micrograms/day) for 2.5 days, PCREB immunostaining was completely abolished in parvocellular CRH-producing neurons after ether or handling stress. Dexamethasone had no apparent effect on CREB immunostaining. These results demonstrate that glucocorticoids suppress CREB phosphorylation in hypophysiotropic CRH neurons and suggest that prevention of CREB phosphorylation is a possible mechanism for feedback inhibition of CRH biosynthesis by glucocorticoids.