Effect of Induction of Inducible Nitric Oxide Synthase on the Blood-Brain Barrier in the Rat

Abstract

Nitric oxide (NO) has been found to have a crucial role in the development of ischemic brain damage and of endotoxin shock. This study observed vascular changes and elucidated mechanisms of development of the brain damage during induction of inducible nitric oxide (iNOS). Five male Sprague-Dawley rats weighing 250–300 g were used. They were anesthetized with a-chloralose and urethane and ventilated with room air. The brain cortical blood flow (CoBF) in the parietal cortex supplied by the right middle cerebral artery (MCA) was recorded by a laser Doppler flowmeter. CoBF and systemic blood pressure were continuously recorded before and after an intraperitoneal injection of Escherichia coli lipopolysaccharide (LPS) (4 mg/kg body weight). Three hours after injection of LPS, horseradish peroxidase was injected intravenously. One hour later the animals were deeply anesthetized and per-fused with 5% glutaraldehyde. The whole brain was dissected and frozen sections of the deep frontal cortex were incubated with HRP using the method of Graham and Karnovsky, postfixed in osmic acid, then processed and observed with an electron microscope. A simultaneous electron microscopic NADPH-diaphorase histochemistry assay was performed on these sections. The blood pressure was significantly decreased about 30 min after LPS administration and a sustained increase (about 30%) in CoBF was observed. The HRP deposits were observed as dark clusters at the outer edge of the endothelial cells. NADPH-diaphorase-positive deposits were observed in the nuclear membranes, endoplasmic reticulum, and mitochondria in smooth muscle and the endothelium. Induction of iNOS may affect the function of the endothelium and smooth muscle as a crucial mediator during derangement of the blood-brain barrier.