Glucocorticoid hormones have powerful multifactorial regulatory effects on every physiological system. Dysregulated patterns of glucocorticoid hormone secretion, often as a result of chronic stress, have adverse effects on physical and mental health. Dysregulation of glucocorticoid secretion is strongly associated with some psychological disorders (e.g. depression and posttraumatic stress disorder) and other biomedical disorders (e.g. Type II diabetes, chronic fatigue syndrome, fibromyalgia). Glucocorticoid secretion is controlled by the neuroendocrine hypothalamic-pituitary-adrenal (HPA) axis system, and the principal factor that has regulatory control over HPA axis activity is glucocorticoid negative feedback. Understanding of the mechanisms responsible for glucocorticoid negative feedback is limited. To address that gap in knowledge, this ongoing research project will determine the molecular, cellular and systems level mechanisms of glucocorticoid negative feedback. This knowledge is necessary to discern how chronic stress leads to altered glucocorticoid negative feedback function, and it will point to new strategies for targeted interventions that will prevent and perhaps reverse alteration of glucocorticoid negative feedback function associated with chronic stress. The guiding hypothesis of this project is that glucocorticoids produce multiple effects within the intrinsic anatomical elements of the HPA axis as well as effects on neural circuits that dictate the moment-to-moment HPA axis activity. These glucocorticoid effects have distinct time frames of onset and expression, as well as separate underlying molecular mechanisms. By establishing these cellular sites of action and temporal patterns of expression this project will determine specific mechanisms of glucocorticoid negative feedback. Previous work on this project identified independent actions of glucocorticoids that are evident within different time intervals after a phasic increase in glucocorticoids that can be distinguished as fast (<15 min), short-term (~ 1 hr), and delayed (~3 hr) negative feedback actions.
Four Specific Aims organized around this conceptual framework will address the following:
Aim 1 ] To determine the temporal requirements and receptor mechanisms by which glucocorticoids produce fast negative feedback at the hypothalamic paraventricular nucleus.
Aim 2 ] To use hypothalamic organotypic cultures to determine cellular and molecular mechanisms by which glucocorticoids produce intrinsic negative feedback on CRH neurons.
Aim 3 ] To determine in vivo mechanisms of glucocorticoid short-term and delayed negative feedback.
Aim 4 ] To determine the relationship between chronic stress adaptation and glucocorticoid negative feedback function. The new information derived from these proposed studies can then be applied to 1) the design of better (more sensitive or revealing) HPA axis related measures and challenge conditions in patient populations, 2) identification of new candidate risk genes associated with HPA axis dysregulation, and 3) development of new treatments that may selectively normalize HPA axis function without disturbing appropriate glucocorticoid signaling throughout the body.
Abnormal glucocorticoid hormone secretion patterns are a major mediator of adverse effects of stress on physical and mental health. This project will explore whether a component of these adverse effects depends on glucocorticoid regulation of neural circadian function. In addition, this project will determine mechanisms that lead to glucocorticoid hormone dysregulation, and thereby provide the basis for new treatments designed to normalize glucocorticoid hormone secretion patterns.
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