SAT-361 Rapid Glucocorticoid Regulation of Adrenoreceptor Trafficking Desensitizes CRH Neurons to Noradrenergic Activation

Stress activates the hypothalamic-pituitary-adrenal (HPA) axis via excitatory noradrenergic projections from the brainstem to corticotropin releasing hormone (CRH) neurons in the hypothalamic paraventricular nucleus (PVN). The resulting systemic release of glucocorticoids feeds back to the hypothalamus to rapidly suppress HPA activation. Patch-clamp electrophysiology experiments revealed a strong increase in excitatory currents via alpha 1 adrenoreceptor (AR1a) activation, which was desensitized after acute restraint stress or glucocorticoid application. This rapid desensitization was reversed by inhibiting endocytosis, suggesting that desensitization was achieved by AR1a internalization. Live cell imaging of AR1a-GFP in a hypothalamic cell line (mHypoE-N42) revealed a glucocorticoid facilitation of norepinephrine (NE)-induced AR1a internalization. FRET interactions between AR1a-GFP and endocytic markers labeled with dsRed revealed that glucocorticoids prevent rapid recycling of AR1a to the plasma membrane, forcing the receptor further down the endocytic pathway. Glucocorticoid treatment also caused an increase in ubiquitination of the trafficking protein beta arrestin, without affecting phosphorylation of the beta arrestin or AR1a. Thus, glucocorticoids likely cause rapid ubiquitin modifications to beta arrestin that shuttle AR1a to the late endosome and prevent it from recycling to the membrane, desensitizing the neurons to NE. The desensitization was found to last at least 4 hours in both ex vivo slice preparations and in vivo stressed animals with elevated blood corticosterone levels. Long term desensitization specifically to noradrenergic inputs could contribute to a systemic stressor-selective negative feedback regulation of the HPA axis.