Abstract 386: Reactive Oxygen Species Mediate Sympatho-Excitatory Responses to Central LPS Challenge in Rats
Introduction: Reactive oxygen species (ROS) play a critical role in inflammatory responses by regulating cytokines, cyclooxygenase-2 (COX-2) and prostaglandin E2 (PGE2). The role of brain ROS in mediating the acute sympatho-excitatory response to inflammatory challenge has not been studied.
Hypothesis: Brain ROS mediate the sympatho-excitatory responses to LPS challenge by increasing central cytokines and stimulating COX-2 activity and PGE2 synthesis.
Methods: In anesthetized rats, we recorded renal sympathetic nerve activity (RSNA), mean arterial pressure (MAP) and heart rate (HR) at baseline and for 4 hours after intracerebroventricular (ICV) injection of LPS, with or without ROS inhibition. Cerebrospinal fluid (CSF) and hypothalamic tissue were then collected for molecular and immunohistochemical analysis.
\Results: ICV injection of LPS (5 μg, n=5– 8/group) elicited significant (p<0.05, vs baseline) increases from baseline in RSNA (44.2 ± 7.2%), HR (97.2 ± 21.6 bpm) and MAP (13.9 ± 2.5 mmHg). LPS significantly (p<0.05, vs vehicle) increased mRNA for hypothalamic NAD(P)H subunits p47 phox (278%) and gp91phox (123%) and NAD(P)H-oxidase dependent superoxide generation (220%); intracellular superoxide production (342%) in the paraventricular nucleus (PVN) of hypothalamus, as detected by dihydroethidium (DHE) staining, also increased. ICV LPS increased (p<0.05, vs vehicle) hypothalamic tumor necrosis factor (TNF)- α (519%) and COX-2 (240%) mRNA, TNF-α (792%) and PGE2 (189%) levels in CSF, and PVN neuronal activation as indicated by c-fos expression (273%). The increases in RSNA, MAP and HR elicited by ICV LPS were significantly (p<0.05, vs LPS alone) diminished by continuous (4 hr) ICV infusion of the O2− scavenger tempol (0.5 mg/10μl/hr, n=5) or the NAD(P)H oxidase inhibitor apocynin (60 μg/10μl/hr, n=5). ICV infusion of tempol significantly (p<0.05, vs LPS alone) diminished LPS-induced DHE fluorescence and c-fos expression in PVN, hypothalamic TNF-α and COX-2 mRNA, and TNF-α and PGE2 levels in CSF.
Conclusion: Brain ROS are pivotal mediators of the sympathetic and cardiovascular responses to central inflammatory challenge, likely by increasing the expression of pro-inflammatory cytokines, COX-2 and the biosynthesis of PGE2.