Ultraviolet laser light of sufficient power can induce focal oedema in the brain. The formation of ultraviolet-induced vasogenic oedema was monitored by observing real-time changes in the integrity of the blood-brain barrier. The brain surface of guinea-pigs injected with Evans blue was exposed to light from a continuous wave argon laser at 351 nm, delivered via an optical fibre. The integrity of the blood-brain barrier was evaluated by measuring surface reflectance using a separate probing light. The brain was then sectioned and examined using light and electron microscopy. Extravasation of Evans blue following vasodilatation was observed when the irradiation intensity was greater than 0.64 W/cm2. The extent of glial and vascular damage could be correlated with the laser power. Irradiated vascular endothelium exhibited lipping at the tight junction, vacuolation and mitichondrial swelling. These results suggest that disruption of the blood-brain barrier induced by ultraviolet light is preceded by vasodilatation.
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