Rationale: Angiotensin (Ang) II exerts diverse physiological actions in both the peripheral and central neural systems. It was reported that the activity of Ang II is higher in the nucleus tractus solitarii (NTS) of spontaneously hypertensive rats (SHRs) and that angiotensin type-1 receptors are colocalized with NAD(P)H oxidase in the neurons of the NTS, resulting in the induction of local reactive oxygen species production by Ang II. However, the signaling mechanisms of Ang II that induce

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... tension remain unclear. Objective: The aim of this study was to investigate the possible signaling pathways involved in Ang II-mediated blood pressure regulation in the NTS. Methods and Results: Male SHRs were treated with losartan or tempol for 2 weeks, after which systolic blood pressure was observed to decrease significantly. Dihydroethidium staining showed many cells with high reactive oxygen species in the NTS of SHRs. The addition of losartan or tempol decreased the numbers of reactive oxygen species-positive cells in the NTS. The systemic administration of losartan or tempol reduced the systolic blood pressure and increased NO production. Immunoblotting and immunohistochemical analysis further showed that inhibition of Ang II activity by losartan or tempol significantly increased the expression extracellular signal-regulated kinase (ERK)1/2, ribosomal protein S6 kinase (RSK), and also increased neuronal NO synthase (nNOS) phosphorylation. RSK was also found to bind directly to nNOS and induce phosphorylation at the Ser1416 position. Conclusions: Taken together, these results suggest that the ERK1/2-RSK-nNOS signaling pathway may play a significant role in Ang II-mediated central blood pressure regulation. (Circ Res. 2010;106:00-00.) Key Words: angiotensin II Ⅲ nucleus tractus solitarii Ⅲ neuronal nitric oxide synthase Ⅲ ribosomal protein S6 kinase Ⅲ reactive oxygen species T he nucleus tractus solitarii (NTS), which is located in the dorsal medulla of the brain stem, is the primary site of termination of the vagus and glossopharyngeal nerves. The NTS participates in cardiovascular, gastric, and gustatory control. Our previous studies demonstrated that several neuromodulators are involved in cardiovascular control of the NTS, including ATP, 1 adenosine, 2 neuropeptide Y, 3 angiotensin (Ang) II, 4 NO, 5 carbon monoxide, 6 and insulin. 7 Ang II is a powerful vasoconstrictor in the peripheral blood system that exerts effects on the central nervous system, regulating fluid balance and the secretion of aldosterone. Hyperactivity of Ang II has been shown to play a major role in hypertension. 8, 9 Ang II is produced from enzymatic cleavage of angiotensinogen by renin and then by angiotensin converting enzyme. These pathological and physiological actions of Ang II are mediated through its type 1 receptor (AT 1 R). 10 Recent evidence suggests that hyperactivity of the brain renin-angiotensin system may play a critical role in mediating hypertension in spontaneously hypertensive rats (SHRs). 11 Significant differences in AT 1 R density were seen in the NTS of SHRs and Wistar-Kyoto (WKY) rats, as SHRs had higher expression levels than WKY rats. 11 The term "oxidative stress" describes chronically elevated levels of reactive oxygen species (ROS) and is associated with cardiovascular disease. 12 ROS play a role in central autonomic networks that are involved in Ang II-mediated signaling. 13 NAD(P)H oxidase is the main source of Ang II-induced ROS in neurons. 14 NAD(P)H oxidase is composed of 2 catalytic subunits (gp91 phox and p22 phox ) and 4 regulatory subunits (p47 phox , p40 phox , p67 phox , and Rac1). Importantly, gp91 phox and AT 1 R are colocalized in the neurons of the NTS, facilitating local ROS production by Ang II. 15