Stress is strongly linked to depression and increased basal activation of the main stress hormone system, the hypothalamic pituitary adrenal (HPA) axis, has been found in approximately 30% of patients with major depression. Glucocorticoids act through two different receptor systems, the mineralocorticoid receptor (MR) and the glucocorticoid receptor (GR). Most work in depression has focused on GR with the traditional dexamethasone suppression test (DST). But, there are a number of reasons to expect that MR may be relevant for depression. Studies have suggested that the balance of MR to GR activity is important not only in regulating the HPA axis, but also particularly relevant to brain serotonin systems. Cortisol, acting through MR has been shown to regulate 5HT1a receptors, which have been shown to be down-regulated in brain in patients with major depression in both post-mortem and neuroimaging studies. Stress and increased cortisol, acting through GR, have been shown to increase 5HT2a receptors, which are also increased in patients with depression. We propose to characterize major depression in terms of MR and GR activity. Specifically, we propose: 1 To extend our previous findings of increased MR activity in subjects with major depression, as assessed by the ACTH and cortisol response to a spironolactone challenge. Based on our pilot data, we hypothesize that MR activity will be increased in patients with major depression compared to control subjects in response to both AM and PM spironolactone challenge. To determine if increased MR activity as assessed by the MR antagonist spironolactone is accompanied by decreases in GR activity is the same individuals, as assessed by the GR agonist dexamethasone, in subjects with major depression. We hypothesize that depressed patients will show GR downregulation and thus increased plasma ACTH and cortisol levels following dexamethasone challenge. Combined with enhanced MR activation, this will lead to an alteration in MR:GR balance. 3.To determine if MR dysregulation is involved in the hypercortisolemia of depression. We hypothesize that normal subjects will show increased cortisol, compared to placebo day, in response to 2 doses of spironolactone while depressed patients will show a smaller increase in response to the 2 dose spironolactone challenge. 4. To determine if MR plays a role in stress regulation in humans. We will examine response to the Trier Social stress test and determine if the there are differences in the ACTH and cortisol response to the TSST in the presence of spironolactone vs placebo. We will conduct these studies in the PM only, the time when the TSST response is most robust, and when MR is believed to play the predominant regulatory role.
Stress plays an important role in depression and the prototypical stress hormone, cortisol, is increased in patients with depression. Cortisol binds to 2 different receptors, MR and GR. But studies to date have only really examined GR function in depression. We propose to characterize the role of MR and the MR:GR balance in depression.
| Medina, Adriana; Seasholtz, Audrey F; Sharma, Vikram et al. (2013) Glucocorticoid and mineralocorticoid receptor expression in the human hippocampus in major depressive disorder. J Psychiatr Res 47:307-14 |
