Huang, P.; Yousefzadehkharvanagh, N.; Simet, D.; Chen, X.; Li, Y.; Larson, R.; Bi, L.; Chen, Q.; Chen, B.; Shan, Z.

Background: Hyperactivity of the orexin system has been implicated in hypertension; however, the long-term impact of orexin 1 receptor (OX1R) overexpression in the paraventricular nucleus (PVN), a key brain region involved in arterial blood pressure (ABP) regulation remains unclear. This study examined whether chronic OX1R overexpression in the PVN alters cardiovascular, neuroendocrine, and oxidative functions. Methods: Adult male Sprague Dawley (SD) rats received bilateral PVN injections of AAV2-OX1R or control virus (AAV2-GFP). ABP and heart rate (HR) were monitored for eight weeks using radiotelemetry. Renal sympathetic nerve activity (RSNA) and ABP responses to PVN administration of orexin A were assessed using in vivo recordings. Reactive oxygen species (ROS) were quantified using MitoProbe, and gene expression was analyzed by qPCR. Primary neuronal cultures were used to explore the mechanisms underlying increased ROS production and neuronal activity. Results: PVN OX1R overexpression increased mean ABP (~10 mmHg), water intake, and ROS levels in both the PVN and peripheral organs. In addition, orexin A evoked exaggerated RSNA (155% vs. 73%) and pressor responses (27 vs. 16 mmHg) in PVN OX1R overexpressing rats compared with control rats; these effects were attenuated by the OX1R antagonist SB408124. Plasma vasopressin levels were elevated, and brain sections confirmed increased ROS in OX1R-positive neurons. In vitro experiments further demonstrated that orexin A upregulated ROS generating enzymes, suppressed antioxidant gene expression, and enhanced neuronal excitability. Conclusion: Chronic PVN OX1R overexpression induces oxidative stress, sympathetic overactivity, and elevated plasma vasopressin levels, contributing to the development of hypertension. Targeting PVN OX1R signaling may therefore provide a therapeutic strategy for hypertension.