orticoids have been considered as a potential cause of stress-induced depression. Glucocorticoids receptor and MR are the two main receptors mediating 3006665 the stressful effect of glucocorticoids. Decreased level of GR in the hippocampus has been found as the primary etiology of HPA axis hyperactivity in depression. However, there is no direct evidence demonstrating that glucocorticoids account for chronic stressinduced depressive behaviors and the hyperactivity of HPA axis. Metyrapone, a synthetic steroidogenesis inhibitor, inhibits the synthesis of corticosteroids by blocking the function of 11-b-hydroxylase, the enzyme responsible for converting deoxycorticosterone to CORT within the adrenal cortex. Metyrapone is used to inhibit the synthesis of CORT under stressful state and attenuate the stressful effect. In the present study, we used metyrapone in combination with chronic mild stress model of depression to investigate whether glucocorticoids account for chronic stressinduced depressive-like behavior and HPA axis hyperactivity. nNOS is the main synthesis enzyme of NO in the hippocampus. Previously, our research identified a novel pathway, MRnNOS pathway, in the hippocampus mediated the stress-induced depressive behaviors. Glucocorticoids up-regulate nNOS expression which then synthesizes excessive NO. NO regulates the function of gene, lipid and protein by soluble Cilomilast guanlylyl cyclasecyclic guanosine monophosphate pathway. Furthermore, NO react with superoxide O22 radical to generate peroxynitrite, which also can regulate the function of several molecules. Intrahippocampal excessive NO disrupts the function of GR, which is proved as a key molecule mediating the negative feedback modulation of HPA axis, by sGC-cGMP and ONOO pathway. Here, we investigated the exact roles of glucocorticoids in the hippocampus and hypothalamus in the development of the pathology of stress-induced depression and whether the proved pathway exists in both tissues. By using metyrapone, our results demonstrated that chronic stress-induced persistent glucocorticoids elevation was required for chronic stress-induced hyperactivity of HPA axis and depressivelike behavior. More importantly, we found that the chronic exposure of glucocorticoids in the hippocampus led to the disruption of the feedback modulation mechanism of the HPA axis and depressive-like behavior, but the chronic exposure of glucocorticoids in the hypothalamus did not induce HPA axis hyperactivity and depressive-like behavior. The MR-nNOS-NO pathway mediated the different roles of glucocorticoids in the hippocampus and hypothalamus. To our knowledge, this is the first time to suggest only the negative feedback regulation of HPA axis 
by the hippocampus is impaired and account for the hyperactivity of HPA axis while the negative feedback regulation of HPA axis by the hypothalamus is not changed. Although the acute exposure of glucocorticoids both in the hippocampus and hypothalamus onset the negative feedback regulation of HPA axis, the chronic glucocorticoids 16476508 elevation in the hypothalamus can’t disrupt the negative feedback regulation owing to the lack of MR expression. This research reveals how glucocorticoids in different places in the brain are implicated in depression and would shed light on the recognition of the not-fully-understand role of the hypothalamus in the stress-induced pathology of depression. Materials and Methods Animals Young adult male ICR mice, young adult male homozygous nNOS-defic
