SAT-362 Hypothalamic Pituitary Adrenal Axis Dysregulation Alters Central and Peripheral Adaptation to Repeated Stress Exposure in Mice

Abstract

Aims: The hypothalamic pituitary adrenal (HPA) axis is the key neuroendocrine mediator of the stress response and controls many aspects of physiology and behavior. We previously showed that experimentally disrupting normal HPA function in mice led to altered neural and behavioral responses to acute stress. When exposed to prolonged or repeated stress, organisms undergo adaptation in many processes of metabolism, endocrine function, and behavior. Further, many of these processes are thought to be driven by HPA secreted hormones. In this study, we aimed to test this hypothesis by disrupting normal HPA axis function and measuring metabolic, endocrine, and neural outcomes following repeated stress exposure. Methods: HPA axis function in male C57BL/6 mice was disrupted via noninvasive, oral corticosterone administration, which we have shown blunts hormonal and behavioral stress responses. Mice were then exposed to repeated immobilization stress (2h/d for 14d), during which time body weight was measured to assess metabolic adaptation to stress. Mice were euthanized and adipose tissue, adrenal glands, blood, and brain were collected for analysis. We evaluated the effects of HPA disruption on mass of white adipose tissue and adrenal glands, and determined plasma corticosterone concentrations as a measure of endocrine adaptation to stress. Using RTqPCR we investigated the effects of HPA disruption on the expression of genes related to synaptic excitability in the medial prefrontal cortex (mPFC), a brain region known to regulate behavioral and emotional responses to stress. Results: Repeated stress led to body weight loss in all mice, however body weight loss was exaggerated by HPA disruption, suggesting increased sensitivity to stress. Additionally, this decrease in body weight could not be accounted for by decreased white adipose mass alone, suggesting effects on other tissues caused by HPA disruption. Repeated stress increased adrenal weight similarly in all mice, but only elevated levels of plasma corticosterone in Control mice, demonstrating altered endocrine adaptation to stress after HPA disruption. Finally, we observed increased gene expression of the astrocytic glutamate exchanger xCT in the mPFC following repeated stress only in HPA disrupted mice, suggesting that HPA disruption affects processes of neural adaptation. Conclusions: HPA axis disruption increased sensitivity to metabolic outcomes of repeated stress exposure and altered endocrine stress adaptation. Additionally, effects on mPFC gene expression suggest altered neural adaptation to stress. These results support the hypothesis that an intact HPA axis is crucial in mediating adaptive responses to stress, and that dysfunction of this system may be linked to negative health outcomes of stress exposure. Sources of Research Support: NSF 1553067 and NIA R21AG050054 to INK.