4. MEU ANO SUSTw 5. FUNOINo NUMNIRS CUMULATIVE EFFECT OF REPEATED BRIEF CEREBRAL ISCHEIA G AFOSR-90-0269

I3. A&STRACT (Mawnum JOG woW We have investigated the problem of Gz-induced blackout in an animal model in which controlled brief global cerebral ischemia is produced repeatedly at short intervals. The objective was to determine if this results in cumulative impairment of brain metabolism and electrical function and if so to identify the mechanisms involved. Our intial hypothesis was that accumulation of lactate may be an important element in this process. Rats were prepared for experiment under halothane anesthesia with trach;ostomy, ligation of both subclavian arteries, cannulation of one femoral artery and of one common carotied artery in cephalad direction. Both external carotid arteries were ligated. Both mouth and rectal temperatures were monitored with ther-mocouples and mouth terperature was maintained at 37.0+0.5 degrees Celsius. A balloon in cuff was placed around the remaining carotid artery. The rat was placed within th spectrometer magnet operating at 4.7 Telsa for lactate and phosphorous. Repeated brief episodes of global brain ischemia were made by temporary inflation of the carotid balloon while MR proton spectra are being acquired serially at intervals of 30 seconds using at 1 cm surface coil. We report results using a newly constructed doubly tuned probe enabling interleaved acquisition of 31P (high energy.phosphate