Brain Receptor Function in Post-Traumatic Stress Disorder

We propose to investigate the underlying mechanisms that account for neurobiological dysregulation of HPA axis function in PTSD. Paradoxically, low or normal plasma and urinary cortisol despite high corticotrophin releasing hormone (CRH) levels are a major feature of this disorder. Some investigators report decreased hippocampal volume in patients with PTSD. The mechanisms responsible for these alterations are not known. One possibility is that patients with PTSD have an increased number of glucocorticoid receptors (GR) and/or increased GR sensitivity, causing hyper-suppression of HPA axis. Another possibility is that high CRH levels lead to increased mineralocorticoid receptor (MR) levels and this up-regulation of MR is responsible for the low cortisol secretion seen in PTSD. Elevated CRH levels could also result in reduced hippocampal volume. In order to evaluate MR and GR function, we will examine the effect of RU486 (Mifepristone; a GR antagonist), spironolactone (Aldactone; an MR antagonist), and placebo, on cortisol and ACTH plasma levels in patients with PTSD, trauma exposed, and non-trauma exposed healthy controls. The extent of increase in cortisol and/or ACTH after administration of antagonists will reflect the inhibition ordinarily imposed by GR and MR. We will also examine subjects' cerebral spinal fluid (CSF), CRH levels, and hippocampal volume. Following this evaluation, patients with PTSD will be treated with paroxetine for 8 weeks. The assessments performed before treatment will then be repeated. The first aim of the present study is to elucidate the pathophysiology of PTSD through the examination of the roles of GR and MR in maintaining PTSD HPA axis dysregulation. The second aim is to compare CSF CRH levels across groups in an effort to extend previous findings and determine whether CRH levels in PTSD are higher than levels in trauma exposed healthy subjects. The present investigation will also evaluate the relationship between CRH levels in PTSD, MR/GR function, hippocampal volume and hippocampally-mediated cognitive tasks. Finally, we will examine the effects of long-term paroxetine treatment in PTSD on HPA axis function, hippocampal volume, and hippocampally-mediated cognitive tasks.