Horseradish peroxidase as a cytochemical marker of blood-brain barrier integrity in oxygen toxicity in the central nervous system

The ultrastructural integrity of endothelial tight junctions in cerebral microvessels of the rat exposed to hyperbaric oxygen was examined to find whether or not there are alterations of the blood-brain barrier in the initial phase of central nervous system oxgen toxicity. Rats were pre-implanted with cortical electrodes for continuous EEG and provided with two polyethylene canulae inserted into the common carotid artery. HRP was administered to unanesthetized rats through a cannula directed into the brain, before the onset of O₂ pressurization. As soon as the early electrical discharges of oxygen toxicity were recorded (20 to 30 min), the animal was killed by injection with saturated KCl into the heart. Examination of small blood vessels in both LM and EM did not support the possibility that the blood-brain barrier is altered prior to the first electrical discharge appearing in central nervous system oxygen toxicity.