Confocal laser scanning microscopy (CLSM) was used to investigate dynamic aspects of rhodamine 6G-labeled leukocytes in the pial microcirculation during the early phase of pneumococcal meningitis. Closed cranial windows were implanted into anesthetized rats without removing the dura mater. Leukocyte behavior was studied every hour after intracisternal (ic) injection. The number of adherent and extravasated leukocytes was determined during playback of videotaped images. Compared with results in controls, the number of adherent leukocytes increased significantly (P < .05) within 1 h after ic pneumococcal challenge, followed by a further increase up to 6 h after infection. In untreated infected rats, the number of extravasated leukocytes progressively increased from 3 to 6 h after infection. Leukocyte adherence to microvascular endothelium occurred in pial venules but not in arterioles. Dexamethasone pretreatment significantly (P < .05) attenuated leukocyte adherence and transendothelial passage of leukocytes.
This study investigated whether the 21-aminosteroid U74389F, an inhibitor of lipid peroxidation, attenuates pathophysiologic changes in experimental pneumococcal meningitis. Infected rats injected intravenously with vehicle and U74389F developed increases in regional cerebral blood flow (rCBF), intracranial pressure (ICP), brain water content, and white blood cells (WBC) in cerebrospinal fluid (CSF) within 8 h after intracisternal challenge. Pretreatment with or administration of U74389F 4 h after infection significantly reduced the increase in ICP but had no effect on rCBF increase. Moreover, U74389F pretreatment significantly reduced brain water content and CSF WBC count. In vitro, U74389F inhibited iron-dependent lipid peroxidation of astrocyte cultures and the production of tumor necrosis factor-a, interleukin-6, and nitric oxide by stimulated macrophages. These data suggest that U74389F modulates early pathophysiologic alterations in experimental pneumococcal meningitis.Animal models of bacterial meningitis have increased our knowledge of the complex pathophysiologic mechanisms of the disease [1][2][3][4][5]. In a rat model of meningitis, we showed that intracisternal (ic) inoculation of live pneumococci or pneumococcal cell wall components induces an early increase in regional cerebral blood flow (rCBF), intracranial pressure (lCP), and brain water content [6]. Pretreatment with free superoxide dismutase (SOD), polyethylene glycol (PEG)-conjugated SOD, deferoxamine, and catalase greatly attenuates these pathophysiologic changes; the strongest effects are shown with SOD and PEG-SOD [6][7][8]. Findings by other investigators support a role for reactive oxygen species in the pathophysiology of bacterial meningitis [9,10]. Cellular injury caused by reactive oxygen species may involve direct damage to proteins and DNA as well as lipid peroxidation [11]. Here we tested the effect of the novel 21-aminosteroid U74389F [12,13], an inhibitor of lipid peroxidation, for its capacity to alter rCBF, ICP, and brain edema formation and to reduce meningeal inflammation in experimental pneumococcal meningitis. Materials and MethodsAnimal preparation. We used a well-characterized rat meningitis model that has been described in detail [6]. Adult male Wistar rats (250-330 g) were intraperitoneally anesthetized with 100 mg! kg thiobutabarbiturate (lnactin; Byk Gulden, Konstanz, Germany), tracheotomized, and artificially ventilated (small animal ventilator, model 683; Harvard, South Natick, MA). End-expiratory CO 2 was continuously monitored by infrared CO 2 analyzer (model 2200; Heyer, Bad Ems, Germany). Mean arterial blood pressure (MABP) was measured by pressure transducer (Statham P23; Viggo-Spectramed, Oxnard, CA) connected to the femoral artery cannula. Arterial blood gases and hematocrit were determined before ic inoculation and every 2 h thereafter (gas check model 1304; Instrumentation Laboratory, Kirchheim, Germany). Body temperature was maintained at 38°C by a rectal thermometer-controlled heating pad. Rats were place...
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