Blood-brain barrier disturbance following localized hyperthermia in rats.

We investigated the morphological effect of hyperthermia on the blood-brain barrier (BBB). The heads of rats were heated locally using flood-lamps. BBB changes were assessed morphologically with horseradish peroxidase (HRP). Histological examinations were carried out 2 and 6 h, 1 and 3 days, and 1 week after the hyperthermia. The acute thermal lesions had three zones, i.e. a necrotic zone, a reactive zone and a permeable zone of viable brain tissue. HRP extravasation was seen in the necrotic zone and the permeable zone. Electron micrographic observation revealed HRP had entered the CNS through damaged endothelial cells and disruption of the tight junctions in the necrotic zone, and through numerous pinocytotic vesicles in the permeable zone. BBB opening to HRP was observed from 6 h to 3 days after hyperthermia.