Blood glucocorticoid levels rise in response to stress activation of the hypothalamic- pituitary-adrenal (HPA) axis. They feed back onto the brain, where they exert both rapid and delayed inhibitory effects on HPA axis activation, corresponding generally to non-genomic and genomic actions, respectively. Dysfunctional glucocorticoid negative feedback is associated with a wide variety of disorders, including stress disorders and metabolic syndrome. The general goal of this project is to determine the site and mechanisms of rapid glucocorticoid feedback actions. Our working hypothesis is that rapid glucocorticoid actions in the hypothalamus are important for the integration of neuroendocrine signaling during stress. During the first period of funding of this grant, we identified a novel rapid glucocorticoid action in hypothalamic paraventricular nucleus (PVN) neurons that involves the activation of a putative membrane G protein-coupled glucocorti in PVN parvocellular neurons and both retrograde endocannabinoid and NO release in magnocellular neurons. Endocannabinoids are also released and suppress excitatory inputs in response to depolarization of PVN neurons. Thus, glucocorticoids elicit multiple retrograde signals in PVN neurons, suggesting a divergence in membrane glucocorticoid receptor signaling pathways, and both glucocorticoids and electrical activity elicit endocannabinoid synthesis, suggesting a convergence in the signaling mechanisms activated by these stimuli. In this proposal, we will build on our previous findings with experiments that address the following aims:
Aim 1 is to study the intracellular signaling mechanisms engaged by membrane glucocorticoid receptor actions and depolarization that lead to endocannabinoid and NO synthesis;
Aim 2 is to investigate the role of glia in restricting the extracellular actions of endocannabinoids to glutamate synapses;
Aim 3 is to determine the role of glucocorticoid-indus-related disorders, including depression, hypertension and obesity. Corticosteroids represent a critical endocrine signal activated during the stress response, and they play various roles throughout the body that increase the chance for survival during stress. Corticosteroids have different mechanisms of action, both rapid and delayed, which are mediated ostensibly by different membrane and intracellular receptors. A clear understanding of the differences in the mechanisms and properties of these receptors will allow the development of pharmacological therapies for stress-related disorders, such as anxiety, depression and feeding disorders, with distinct pharmacodynamics and reduced side effects.
Corticosteroids represent a critical endocrine signal activated during the stress response, and they play various roles throughout the body that increase the chance for survival during stress. Corticosteroids have different mechanisms of action, both rapid and delayed, which are mediated ostensibly by different membrane and intracellular receptors. A clear understanding of the differences in the mechanisms and properties of these receptors will allow the development of pharmacological therapies for stress-related disorders, such as anxiety, depression and feeding disorders, with distinct pharmacodynamics and reduced side effects. 1
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