Astroglial swelling for removed rat brain enlargement incubated in deoxygenated mock cerebrospinal fluid

The source and target of edema fluid for ischemic brain swelling clinically often observed in "malignant infarction" was examined in ex vivo. Wister rat brain hemispheres were removed and incubated air-tightly in a deoxygenated artificial cerebrospinal fluid at 37°for 30 min. Ionic movement into the brain tissue was calculated from their concentration changes in the incubation fluid. We found a weight increase by 11.3±2.5% (p<0.01) and a decrease in Na⁺ from 148.0 to 139.0±8.2 mEq/l (p<0.01) and an increase in K⁺ from 4.3 to 11.2±1.2 mEq/l. Video tape recording revealed that the brain swelling started immediately upon the incubation, and the electronmicroscopical investigation of the swollen cortical tissue revealed that the fluid moved mainly into astroglial cells. The astroglial swelling was quite similar to that of specimen taken from clinical cases at autopsy. The driving force of the water shift can be explained by discharge of thermodynamic potential, i.e., a coupled transport of water with Na⁺ across the cell membrane (anomalous osmosis). The swelling was not affected by addition of aquaporin blocker, mercuric chloride. It is concluded that cerebrospinal fluid bathing the brain in situ can be the source of edema fluid for ischemic brain swelling.