Neuronal Fos-like immunoreactivity in ouabain-induced hypertension

In normotensive Wistar rats, systemic administration of exogenous ouabain f or 10 days or more induces hypertension, presumably through central mechani sms. To identify which neuronal populations may be involved, we assessed Fo s-like immunoreactivity (FLI) using an antibody that recognizes the protein products of the fos family comprising Fos, Fos B, Fra 1 and Fra 2, thus en abling detection of chronic neuronal activation. Young Wistar rats received s.c, infusions of either ouabain (50 mu g/day) or saline for 7 or 14 days. At the End of the experimental period, mean arterial pressure (MAP) was as sessed. In a separate set of rats FLI was detected immunohistochemically an d quantified in cardiovascular and osmo-regulating centers. Resting MAP in ouabain-treated rats was significantly higher than in control rats at 14 bu t not at 7 days (125+/-4 vs. 101+/-6, P<0.05 and 102+/-4 vs. 98+/-6 (not si gnificant), respectively). Within the supraoptic nucleus, ouabain induced s ignificant increases in FLI compared with control rats at 14 days (9+/-2 vs . 2+/-2, P<0.05) but not at 7 days. Within the locus ceruleus, FLI was only detectable in rats that received ouabain infusions for 14 days but not in other groups of rats. Ouabain treatment did not induce significant changes in FLI within other areas. These results demonstrate that chronic s.c. ouab ain infusion only increases neuronal FLI in the supraoptic nucleus and locu s ceruleus where increases in FLI parallel the increase in blood pressure. (C) 2000 Elsevier Science B.V. All rights reserved.