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Centrally applied angiotensin II (Ang II) increases sympathetic nervous activity and mean arterial blood pressure (MAP), but the mediation of these effects is not fully understood.To test the hypothesis that central effects of Ang II are mediated by reduced nicotinamide adenine dinucleotide phosphate [NAD(P)H]-oxidase-dependent production of superoxide in the hypothalamus.Under isoflurane anesthesia, male Sprague–Dawley rats were given an intracerebroventricular infusion of either artificial cerebrospinal fluid or apocynin (4 μg/kg per min), a selective inhibitor for NAD(P)H oxidase, for 30 min, followed by Ang II (20 ng) or carbachol (200 ng), while MAP and heart rate were measured at the femoral artery. At the end of the experiments, hydroethidine, a superoxide-sensitive fluorescent dye, was infused intravenously for 10 min, and superoxide production was assessed in the vasoregulatory hypothalamic nuclei using confocal microscopy.Ang II elicited a rapid 11 ± 2-mmHg increase in MAP and a 16 ± 2-beats/min decrease in heart rate. Apocynin abolished these effects of Ang II in a specific manner, as carbachol-induced increases in MAP were unaffected by the inhibition of NAD(P)H oxidase (MAP increased by 9 ± 2 and 8 ± 1 mmHg in the absence and presence of apocynin, respectively). In response to Ang II, apocynin-sensitive production of superoxide increased significantly in the nuclei of the anterior hypothalamus, in the subfornical organ, and in the paraventricular nucleus of the hypothalamus.These findings demonstrate that acute pressor responses of central Ang II are mediated by NAD(P)H-oxidase-dependent production of superoxide in the hypothalamus.