The goal of this proposal is to continue our investigations of the limbic- hypothalamo-pituitary adrenal (LHPA) axis in normal humans and its dysregulation in major depression. there is general agreement that this axis is altered in many subjects suffering from affective disorders, although the nature of the disruption and the sources of variance remain ill understood. During the past 5 years of funding, we have used a combination of peptide measures and challenge paradigms to study the status of the LHPA in depressed subjects and have found that a) following a dexamethasone challenge, a larger proportion of these patients appears disrupted at the level of the pituitary than can be discerned with cortisol measures. b) as a group, these patients are less responsive to secretagogue challenge, regardless of their circulating steroid levels. c) depressed subjects appear to have increased suprapituitary drive, at least in the evening hours, i.e. at the nadir of the circadian rhythm. d) they appear to be insensitive to rapidly rising steroid levels, a feedback mechanism thought to be mediated in the brain, most likely in hippocampus. e) the expression of these disruptions is greatly influenced by two individual variables: age, sex, and their interactions. In this proposal, we attempt to more clearly """"""""isolate"""""""" the elements of the axis by using novel challenge paradigms that focus primarily on pituitary versus brain, in order to investigate their relative contributions to the axis. In order to do so, a number of studies are proposed to calibrate and validate these paradigms in normal controls prior to their use in psychiatric patients. The results will shed light on the normal mechanisms governing LHPA in humans, as well as their alteration in affective disorders.
One aim i s focused on more fully """"""""isolating"""""""" the pituitary by administering simultaneously both secretagogues, corticotropin releasing hormone (CRH) and vasopressin (AVP) while blocking cortisol synthesis. This is followed by studies on the nature of steroid feedback at the level of the pituitary. The remaining paradigms attempt to """"""""move into the brain"""""""" by focusing on mechanisms such as fast feedback which are known to be mediated at a suprapituitary level. We shall investigate the nature of the increased drive, the role of specific glucorticoid and mineralcorticoid receptors (GR and MR) in controlling it, the disruption of fast feedback following a stress challenge, and the contribution of the two receptors in that mechanism. Finally, studies will be carried out in aged and euthymic patients with a history of repeated depressive or manic depressive episodes to determine whether their stress responses become altered even when out of episode. These studies have been shaped by our improved understanding of the LHPA in rat (Project I), and the interpretation of the results will be aided by the funding of the postmortem studies in Project III.
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